Sorry, I know that noises are very hard to describe, let alone diagnose, over the internet. So, maybe someone could point me in the right direction or offer some clues as to what to check/investigate.

'95 F-150 5.0 w/ auto, RWD, ~75K miles, standard cab, long bed.

The noise only seems to occur at highway speeds (60+ mph) and does not seem to get worse the faster I go. I had it up to 80 mph to check. The sound seems to emanate from just behind the radio and just under the center defrost vents in the dash pad. It's loud enough to be annoying and prevents low voice level conversation. I would describe it as a loud "hum" like something is very quickly vibrating but only moving a short distance.

In an effort to figure out if it was heater plenum related, I changed the selector to move air thru the various vent hoses as well as changed the fan speeds. None of these changes seemed to have any effect (I was hoping it was maybe a blend door or something like that).

I have heard what sounds like leaves swirling around in the plenum box but that sound is repetitious (it always sounds the same) so I don't think it's leaves and in retrospect seems unrelated to this. The coolant has been changed and the heat works so I don't think it's air trapped in the heater core (but I may be wrong).

The truck doesn't get driven on a regular basis but I will need to drive it this weekend. And, I will be using it for medium trips (~3 hours each way) as the weather warms. I really don't want to have to listen to that noise for that length of time.

TIA, Dave.

 

This usually means you are low on coolant.

Have you tried pressing on the dash or lifting up on it when the noise is happening to see if you can make it stop. This may not be your problem but look on the right side of the dash where it connects to the a-pillar. It is very common for the dash mount to break in this location and cause vibration and noises.

 

Considering that it doesn't leak, I would not think so. The temperature gauge (I know, I know) always reads low and the reservoir has coolant but I'll check it.
I did try pressing on the dash pad, above the radio, while on the expressway. Granted, I couldn't really drive and apply a lot of pressure but it did not make any difference (wrt to the noise being generated).

When you say "right side of the dash", I am assuming you mean on the passenger side?

Thanks for the thoughts.

One thing I failed to mention previously; I had the windshield replaced last Fall. The noise just started this past weekend so I don't think the two have any commonality.

 

Yes left and right is always judged when sitting in the driver's seat so right = passenger side.

 

I just wanted to be sure, thanks.

 

I did check the dash pad and it seems to be very well connected. It is not loose in any area and all of the support brackets are tightly fastened.

I laid on the floor hoping to look up under the dash and see up to the radio area. Ha! I should have known better and have worked on too many old Mustangs. That area is so densely packed, it's impossible to see much of anything.

I will have an opportunity to drive the truck, with my wife along, this weekend. Perhaps the both of us can figure out from where the noise is emanating and why.

 

Have you done anything to the truck in the engine bay. I was working on mine replacing things and got done and started my truck and had a noise inside I thought ended up being a hose clamp touching the air conditioner dryer but sure sounded like something in the cab.

 

Maybe not related but there is a brace in the dash that breaks and it rattles like crazy. Ford has an updated part to fix it.

 

I have done work in the engine bay, but the amount of time that passed between that work being completed and the noise issue has been almost a year. So, you have a valid point and I'll look things over. That said, read on, I might have found the issue.

 

I think inmate jas88 was referring to that brace. However, I cannot find any portion of the dash that's loose. So, I'm wondering where, exactly, that brace is and what part number I might need to order. I can check with my dealer, they're pretty good (well, the Parts and Service guys, that is).

 

Firstly, I think I've resolved the gurgling issue in the heater core. I ended up adding about 1/2 gallon of coolant to the radiator and the noises have stopped completely. There's a lot more room in the radiator than it appears just by looking into the fill neck. I was really surprised by how much I was able to add.

Secondly, I had an opportunity to drive with my wife in the truck. She was able to pinpoint the source of the noise to the area where the dash meets the passenger side door.

After removing the inside windshield trim (across the top of the windshield), the trim piece along the side of the windshield and above the door and the kick panel, I discovered a lot of loose fasteners and a wear spot where the kick panel appears to have been rubbing on the door trim;

Kick panel:



Door trim:



Those two white spots meet and appear to show a wear pattern. So, I used a heat gun and ball peen hammer to push that area in some, on the kick panel. When I re-installed the panel, it was clear it had not been properly seated (due to vibration/age) and must have been rubbing on the door trim. Now that everything is back together and tight, I'm able to pass a thickness of corrugated cardboard between the two panels. I did not get a chance to go for a test drive however. So, I'll need to do that before I can consider this fixed.

 

Another follow-up: I managed to find a thread post that shows the plastic dash bracket that breaks which allows the dash to shake and make noise(s).

My '95 F-150 appears to have the factory fix (the bracket is metal and a different shape). So, this may never have become an issue, on my truck.