Dear FTE,

When listening to AM radio, I get a "siren" sound from interference somewhere. It sounds like a siren that goes up but never comes down. Very annoying. It only does it when the headlight switch is on (any position) and can be significantly reduced by dimming the dash lights completely. If I turn the headlights off and then back on, it stops for a few minutes. Any ideas?

Signed
Light-ly Annoyed in Midwest

 

clean your battery terminals.....

 

nafzimo

You are not going to like this answer.

The battery terminal post is a good start and might just work but your fairly new truck most likely has a new battery and is solidly connected... but check it any way.

The siren/whine is an induced signal comeing from some other source than the lights (lighting is usually a well grounded DC circuit).

As a HAM radio guy I have installed trancievers in many different vehicles and tracking down interference can be a real pain, especially on these newer vehicles.

Considering you have a 2002 I would first give the Ford dealer a shot at it under warenty. They will probably put in a new radio, maybe even a new light switch. Though I doubt they are the problem.

Does the noise happen only on AM and has it just recently begun. Is it louder at your home or near a particular business. In other words can you tell if it is external or from some power line or industrial outside source? Maybe the microwave at home, or under your house power pole/transformer?

Can you cause this noise in any driving situation or is it only with engine on/off? Stopped or moving? Brakes on or off?

Have you added a amplifier to the stereo system? Any in/under dash tinkering?

My experiance with sensitive Ham radios is that Ford trucks cause interference from the following sources:

1. Electric fuel pump
2. ABS pickups
3. Tone wheel (inside rear end)
4. Alternator
5. Alarm systems
6. PCM
7. Power Amplifiers

Throw me some more info an I will see if we can narrow down the source. Most of the time this is tedious troubleshooting by elimination.

 

On older Fords this was an indication that the Alternator was failing. One or more of the diodes in the Alternator had failed, the alternator would still charge, but amperage output would be lower. Is the noise there without the engine running? Does the noise change with engine RPM?

 

[QUOTE]Originally posted by Fredvon4
The battery terminal post is a good start and might just work but your fairly new truck most likely has a new battery and is solidly connected... but check it any way.

Battery terminals look good... clean and solid.

The siren/whine is an induced signal comeing from some other source than the lights (lighting is usually a well grounded DC circuit).

But it only does it with the light switch on. I can shut off the headlights and have no noise at all.

Does the noise happen only on AM and has it just recently begun.

It has been a problem all along but only on one AM channel.

Is it louder at your home or near a particular business. In other words can you tell if it is external or from some power line or industrial outside source? Maybe the microwave at home, or under your house power pole/transformer?

I have a 37 mile trip to work and it does it the whole way.

Can you cause this noise in any driving situation or is it only with engine on/off? Stopped or moving? Brakes on or off?

I haven't tried driving with the engine off. It does it stopped or moving, and the brakes don't seem to affect it.

Have you added a amplifier to the stereo system? Any in/under dash tinkering?

No new amp. I have installed a remote starter, but it did it before the install. I have the remote starter module removed right now and it is still doing it.
[QUOTE]

 

Sometimes simple things can be hard to think of.

Unfortunatly I have not been motivated to spend the bucks for good shop manuals for the SD truck as mine so far (knock on wood) has not had any problems. That means I have never seen the schematics of these newer trucks.

I have all mechanical switches and old style bi-metal flasher unit on my lighting system on my truck. ( no electronic source of AC or RF)

I am not aware of any light system component that can self oscillate and radiate an AC/RF signal or harmonic of it, that could get into the AM antenna on only one channel or frequency.

Because the squeel/whine is only on a single channel and dimming the dash lights attenuates the noise, there has to be some ACRF signal on the +12V DC side that the light system wires are able to radiate.

Back to some of my previous questions... does it do it with the engine off?

What AM frequency? such as: 1400khz or 870khz?

Do you have an electronic trailer brake controller?

Is it there one channel up or down, even very faintly?

Have you ever removed the dash?

Are you willing to pull the light switch and see if the wires or dimmer potentiometer wiper are not loose?

Have you ever removed the large connector on the engine side firewall to get access to the pcm?

Is this a "weak" AM station that has some natural background hash and noise (not the squeel/whine) or is it very strong most of the time?

I know I am hunting here.

Usually the newer trucks do not have failed Alternators this early but, in this case it is a key suspect as it is one of the first and direct ways for AC to get into the DC system.

As stated by C_Marshall the alt has a diode rectifier bridge and if one or more diodes has failed short, then there will be variable AC hum/whine you can hear in the radio.

But usually this noise is very rpm dependent and I just gotta believe you have heard an Alternator whine before.

 

Does the winsheild wiper motor cause a a whine also as well as the lights sw being on ?

And is their any aftermarket lighting on your truck?

look for loose grounds

Have you washed the engine lately ?

We are all hunting now for ya!

Rich

 

I have only noticed it on 890 am. I drove home with the headlights on this afternoon and could not get it to do it. No engine washing lately. No aftermarket lighting. I do have a prodigy brake controller... I will unplug it and see if I still get the sound. I probably won't drive it to work until Monday though.

Thanks guys!
Matt

 

The radio (6 disk in dash changer) on my '01 F250 has done the same thing a time or two. It has always stopped after turning the radio off, then on again. It is as if this gives a filter a chance to catch up (the analogy that comes to mind).
Strange.

 

Wow, I thought my truck was the only one with this problem... The radio in my 2001 F250 has done a very similar thing since day one. When the vehicle is first started in cold weather (32F or less), the radio makes a "squealing" noise which sounds like RF interference. It doesn't happen in warm weather. The noise varies depending on what kind of load is being placed on the electrical system, e.g. turning on the heater or headlights changes the pitch. The interference seems to be confined to narrow areas in the AM band only, especially ~630 Khz. After driving a few miles the noise goes away.

Interestingly enough, the noise oscillates relative to vehicle motion! The faster the truck gets to rollin', the quicker the noise pulses.

cw

 

i get a solid interferance noize whei i play am and turn the A/C on to max. The noise is loud as hell. Why?

MotoX

 

Motoxman_117

I bet money it does not do it with a cd, tape, or on FM.

The reason it does it on AM is that many DC motors, with brushes, radiate a AC signal that can be some harmonic of the AM receivers tuned channel or frequency. It will get louder the faster the fan is set because there is the full 13.8VDC when on "high".

If you listen closely with the windows up and the fan on low as you "tune" the entire AM band you will find channels (frequencies) where it is louder and others where it is not noticeable. This has been this way since the early 1900s when AM radio was invented.

There are some things you can do to reduce the noise (radio frequency interference (RFI)), but because most folks mostly use cds or FM, there are no longer any good chokes or filters readily available at rat shack or other radio stores.

It is possible to attenuate (reduce) much of this "noise" by simply putting ferrite chokes over the power leads to the electric fan or motor (fuel pump, window motor ect.).

If you have a computer repair shop that does a lot of business then you might be able to get these cheap or free.

What you are looking for are the plastic caged "magnet" shields like are on computer power cords, monitor cables, phone lines, or even printer cables.

Computer repair shops usually have boxes of ODD cables with these on them. The same RFI shields cost $3.00 to $5.00 and can get expensive if you need a few of them.

nafzimo
And others with the noise only with light switch on, and not always duplicate able, or seems to be temp related:

Might be the dimmer pot to the right of the headlight switch is dirty, loose, or vibrating.

Also the design of this potentiometer may be acting like an inductor and "receiving" an AC source within the truck (like the fuel pump motor) and amplifying the signal down the power line and radiating into the front end (antenna) of your AM receiver.

I have several talk radio AM stations that I enjoy, and there are some that when my heater/AC fan is on high have a lot of this same RFI. Annoying, yes, but I just live with it because getting close to the heater fan to try the chokes is a PITA.

My electronic brake controller causes this squeal when I am hooked to the trailer and use the brakes, only on AM 1400khz. Fortunately I am out on the road when hooked up so I loose my KTEM 1400khz station long before the squeal really annoys me.

I have two different HAM radios and assorted antennas. These are fairly sophisticated and well-designed radios, and I did a good job of getting proper grounds, clean DC power so have no F-250 SD induced RFI to chase down.

The relatively cheap AM/FM radios from most companies do not do a good job at noise blanking and have the cheapest possible receivers in them.

They will always be susceptible to RFI, and other than shielding the source, reparing the bad alternator, or eliminating the arcing switches/potentiometers, there is not a lot, if anything, to be done to the radio to eliminate the noise.

Basically saying, don't throw a new radio at a noise problem unless you know that the current radio is faulty.

Also do NOT put the ferrite choke on the radio antenna input. It will attenuate (reduce) ANY RF on the wire and you will have a hard time getting any but the strongest of stations!

 

codywyk

Quote:

"Interestingly enough, the noise oscillates relative to vehicle motion! The faster the truck gets to rollin', the quicker the noise pulses. "


I solved that problem on a fellow hams F-250 by putting a ferrite choke on the cables back at the tone wheel connector on the rear end.

I think the intial squeel may be from the fuel pump, as these tend to be real noisy when they are pumping a lot, then die down as they get warm or perhaps the fuel preasure gets high enough to make the pump cycle less frequently.

 

SOLUTION!!!!

Stop listening to AM radio!!!!



Just kidding!!!

Only experienced this problem back in my early years, when I installed aftermarket amps...Never figured out how to fix it, just turned up the music louder!!!!

 

I agree with Fredvon4 on this one. I believe your sound is being induced by your alternator. The frequency of your noise changes with engine speed or alternator load. The cold temperatures may be effecting the grounding ( bonding ) of your body, hood, electrical components. I would disassemble, clean, and reassemble every ground and bonding wire I could find (scrape the paint off the body). Just don't look at them, take them apart. I know of one bonding wire from the hood to the body just forward of the passenger winshield wiper blade. Also I believe there is another bonding wire under the truck right under the passenger's seat, I'm sure the bed has one somewhere. It has also been mentioned to do the battery cables, insure you do both ends. If this does not work try running a seperate bonding wire from the actual alternator housing to the truck body. When you attach the wire to the truck body try to find a point away from the radio antenna, and the radio it self. This is a trick I used when building competition sound systems many years ago.

Are these Ford factory radio's. Your problem maybe "interstage modulation", this is caused by a cheap tuner design and construction. Most factory radios don't have the greatest specs, "Noise rejection". Pioneer is known for making great aftermarket tuners. If you have noise with a Pioneer then you have real problems.

My .02 worth !

Mark