I have a 2001 F-150 Supercab with the V-6. This past weekend it developed some strange noise best described as a rattle or vibration that sounds like it is coming from under the driver's side dash possibly somewhere right behind the instrument cluster. May even sounds a little like a "grinding" noise - like two plastic gears not agreeing with each other, but I don't know of anything under there that could make that noise. I have opened the hood and listened from there with my wife pressing the gas to make the noise start, but can't hear anything from outside the truck.
It is not constant, but starts as soon as I give it a little gas, even before I put it in drive. It's a little worse when it is in drive. I have turned the air on and off, turned the steering wheel, pressed the brake, etc, and it doesn't appear to be related to anything obvious. I have stuck my hand under the dash and can't find anything obviously loose. Has anyone else had this problem? Any ideas would be appreciated.

 

What happens with the blower on ? Or off ?

Dave

 

OK, I see you tried the A/C, so maybe the blower isn't involved.

Dave

 

Might be vacuum related if it gets a little worse when put into drive (or any other gear).

Try unplugging vac lines, one at a time, and see if the noise goes away ( especially anything on the firewall, under the hood or the dash). Also, if it was vac related, tap the gas pedal a few times to get the RPM's to jump to 2500-3000. The vac will drop pretty low then, so if something is ruptured, the noise should momentarily cease.

Dave

 

It is mostly quiet while just idling. It "rattles" upon start-up. It is at its worst during initial acceleration from a red light - so you could be onto something with the vacuum. When driving, the noise pretty much goes away as speed goes up, almost like it is reaching a "harmonious frequency" of some kind. I'm going outside to look under the dash again.....

 

So I figured out what the noise was. The large bracket bolted to the exhaust manifold on the driver's side with a large eye-hole at the top.
Story: All of a sudden the noise just stopped. When I got home and looked for it, I popped the hood, and the broken bracket was just laying there on top of the frame. Amazing that it stayed there until I got home or I may have never figured it out.
There is one on the passenger's side as well. I don't know what these are for, but they seem to serve no purpose. I assume they are for lifting the engine in and out and are just left there after initial engine installation. It does seem a bit strange to me that a bracket to hold that much weight is bolted on with one exhaust manifold bolt on each side so if this is not what it is for, can someone please let me know.

 

THey are for lifting the motor. Remember steel has a tensile strength of 20,000 pounds per inch. A 3/8 inch bolt will easily hold a ton of weight. Your motor probably weighs 500pounds. Couple small bolts would easily pick it up. Parts get lighter and cheaper every year... or at least cheaper !

 

Heat sure does strange things to stamped steel parts.

 

Yeah, it broke above the bolt hole where it connects to the exhaust manifold - really in a strange place and it seems to be of no consequence. More importantly, it is nice to know that I can come on here and post some off the wall question and there are people that can answer it take the time to do so. Thanks everyone.

 

I have seen stamped steel mounting parts for air cleaner assemblies that were 1/4" thick crack simply mounted above a hot hyd tank on a tractor. Hyd oil maybe 250 degrees. Not just once but many times. I put it down to inferior China steel. LOL