Here's the best I can describe it. When it decides to happen its both a static-y hiss and a whine. The whine varies in pitch and volume depending on not only engine speed but also accessories turned on. Turning on the heater blower motor will make it louder and the more fan speed the louder. Turning on a turn signal will *sometimes* make it louder per click of the signal.

But then it just goes away. It comes and goes very suddenly. The whine is not present with the engine off, but the static-y hiss sound is.

Taking the face plate off the stereo does not affect the noise in any way. Pretty much eliminates noise signal coming from head unit. It HAS to be something affecting one or the other amps or a signal that is being picked up by the wires.

The ground is good. 14.15v at both amps measured across the plate where the cables plug in, 14.26v across both of the batteries while running. Both amps grounded to same spot, which is a tapped hole in the frame with a bolt and a short 2 gauge battery cable bringing the ground into the cab, both amps tied into the cable. HU also grounded to same cable.

RCA cables run along transmission hump. Power line runs under driver's side door sill plate, plenty of space between them.

Both batteries same CCA, brand, purchased at same time. Fluid level looks good, got some distilled water to top them off with just in case.

I think I've looked at all the basics, that's whats driving me crazy.

 

Do you have quality audio equipment and what size amps are we talking about here? From what it sounds like you are describing 2 different sounds or really a variety of sounds. It is starting to sound like a bad ground contact somewhere. When you say the amps are grounded to the frame, do you literally mean the frame rail on the underside of the truck or to the cab? If it's to the cab then I would suggest checking grounds for everything. Hams get really paranoid about grounding things so keep that in mind with my suggestion. If the truck doesn't have cables to ground the bed to the frame, the cab to the frame, and the engine to the frame, then you may want to make some. I immediately think ground because you are talking about several independent systems contributing to the noise factor. Really the only thing they all have in common is chassis ground. But if the grounding points between chassis parts are corroded or broke, then different parts will have different ground potentials and wreck havoc on things. I've never taken a look at the grounding on these trucks, but since you have me thinking about it, when I rebuild mine I will, and I'll beef it up.

Chad

 

Yes, literally to the frame rail. Hole drilled and tapped, bolt threaded through, 2 gauge wire ran into cab and amps grounded to that. Amps themselves are on a formica board and isolated from the cab. It is not a simple ground issue with the amps. I'll check the grounding of the cab and block to the frame.

Components:
Kenwood Excelon KDC-X491 CD Receiver
Infinity Reference 6810cs 5"x7'/6"x8" 2-way Component System for the front
Infinity Reference 6812cf 5"x7"/6"x8" 2-way Speakers for the back
(2) MTX amps, one 50X4, and one 200X1
Kicker Solobaric L5 square 10" sub in truck box


Its the same noise. They do not occur independently. If the hiss is present, it will whine while running. If it whines, the hiss is in the background. Never is there whine without hiss.

 

For giggles, disconnect one componet at a time, and move on depending on the results.. if you have the time..

 

If your amp body is on a formica board and isolated from the cab you may have a ground loop of some sort. I imagine the your HU metal chassis is in contact the metal in the dash, yes? If so, but your amps aren't in contact with the metal of the cab you could cause a ground loop. try to tie in the amp body's to the cab via a ground jumper or possibly use a jumper to tie in a section of the cab close by to your 2AWG frame ground. You may see if installing power filters to your HU and AMP positive lines would alleviate the problem, but double checking your grounds is cheaper. Also you still need good grounds before you install any filters.

Chad

 

An amp should always be mounted on an insulating material, mounting it directly to metal is a great way to get noise. This is also not a new installation, its been in the been mounted like this for quite awhile with no problems, so something had to change to make the noise start. It coinincided nicely with the GPR going out, too, which could just be coincidence, I suppose.

I topped off the battery today, one cell was quite a bit lower than the others, which can sometimes cause a noise issue. I also ran a grounding strap from the cab to the frame. The bed is already grounded to the frame though a hide-away ball hitch in the bed. I didn't get a chance to crawl around and see if the factory motor ground is still in good shape, but that'sll be the next step if the problem persists.

I'll see Sunday if it cleared it up, first time I've got a decent drive ahead of me.

 

Well, I fixed it. I'm still not sure what I fixed, but topping off the battery and installing the ground strap from the cab to the frame seemed to fix the noise. 3 hours in the truck and no noise at all, my blood pressure can return to normal.

I'm still just wondering what was broadcasting the noise, or in other words what wasn't grounded properly before. Its apparently not something in the audio system, so I was getting interference from something else that's grounding out on the cab.

 

Thanks for posting, I was wonder how you were doing with this.. I would have never expected the topping off of a battery though.. Good call

 

Do you have an iPod cord or USB cord hanging from your stereo? On mine sometimes when I don't have anything connected to it it picks up noise like yours. Just an idea.

 

Yeah, me either. I was surfing for things to try, and that came up. Sure enough one of the cells was low.

Since I did the grounding strap at the same time, its tough to say which one (or both) cleared it up, but it's back to really clean sound like it was originally. No noise, hiss, hum, etc.