For about the past 6 months now, my truck makes a resonating humming sound for about the first 5 minutes of driving every morning, BUT ONLY IF AT A COMPLETE STOP, IN GEAR, FOOT ON BRAKE. If I release the brake and start to move, or if I put it in nuetral, then the noise stops. I've had it into the dealership 2 or 3 times for it, and every time they just see my aftermarket exhaust and immediately blame it on that. So over the weekend, I went through the time & expense of replacing my muffler TWO TIMES. I initially had a Gibson, then switched out to a DynoMax, and then to a 30" Magnaflow... Well needless to say, the hum is still there. And it's quite irritiating. I've tried to trouble-shoot it, but to no avail. I don't think it has to do with the engine or the exaust, because I've let it sit and idle for 20+ minutes before driving it, and it still makes the noise... And it's obviously not the exhaust (3 mufflers & piping later)...

The sound seems to be coming from somewhere near the rear of the truck. I thought maybe it was the rear differential, but everyone says the diff can't make noise if it's not moving (makes sense).

So I'm really at a loss here. The dealership isn't willing to help because they believe it's caused by my modded exhaust (and the noise does appear to be coming from that vicinity). I'm just getting very tired of this, and although it only happens for the first ~5 minutes of each day, it's still very unpleasant and irritating. So does ANYONE have any suggestions on what might be causing this?????? I've though about the 'vibe' TSB's, but I don't think my symptoms are the same, as the noise stops once the truck begins to move... HELP!!!!!!!!!

 

Sounds like some form of resonnat vibration. They make an exhaust dampener that consisits of a weight that is fastened to the system to quench vibrations. You might give that a try. Also, make sure your spare tire is cranked up good and tight and that it is not touching anything that it shouldn't be.

 

The exhaust dampner that you mentioned, where do I get it from? Is it only from Ford, or is it aftermarket? Auto Zone? Pep Boys? Ford dealership? Thanks for the suggestion, I definately want to give it a try.

 

You say it is not coming from the rear. Sounds like an air box noise. Lots of air cleaner setups make noise cold.

Get an assistant to sit in the truck and make the noise while you walk around with the hood up and look for the sound.

Try shaking or re tighten the air box, pull the air filter out and put it back. See if that has any affect.

Look for clamps touching anything on the exhaust.

Loosen up the exhaust clamps and see if it makes any difference. Don't forget to re tighten after.

 

i had that too...

it was the air intake tube that connects to the right side of the engine bay and the airbox.

I tightened it with some zip ties in a crazy arrangement...

 

It IS coming from the rear of the truck. I did also have the air intake tube rattle, but solved that long time ago (thanks to you guys)... Anyway, again, it seems to be emanating from the rear of the vehicle, around the muffler/drive shaft/rear diff, etc...

I'm very interested to hear more about an exhaust dampner...

 

Could it possibly be the electric fuel pump?

 

The exhaust dampener is one or more weights shaped to fit on the exhuast pipe which may be clamped on at different locations to absorb unwanted vibration. They can be attached with a hose clamp or a u-bolt. Dealerships use them but I would expect that any reputable exhaust shop should be able to tell you where to get them.

 

One thing that really puzzles me is, why does it go away after ~5 minutes of driving???

 

It is the fuel pump......
Always have atleast a 1/4 tank of gas to keep the pump cool.
Google "buzzing fuel pump"

 

So I just called 3 of the best-known muffler shops in the area, and none of them had ever heard of an exhaust dampner. What gives?? Does anyone know if they're available at auto part stores?

 

An exhaust damper is tuned to the specific exhaust system. For example, if your problem frequency is at, say, 32 Hz, then the damper will be a cantilevered weight that will vibrate in the opposite direction as your exhaust and cancel out the noise. There probably won't be a general damper that will be available at your local Pep Boys, Autozone or whatever parts store you use.

I don't recall the F-150 requiring a damper anyway. The system is heavy enough and secured in multiple locations such that it should not vibrate in the resonant range of the system. Just my opinion.

Now, speaking as an engineer, specifically a powertrain engineer with Ford, I will suggest that you put your stock system back on to verify that the noise is still there. If it is then you can clearly show the dealer that your aftermarket exhaust is NOT the problem and that they should diagnose the problem.

Another suggestion...have them check the t-case fluid. If it is low then there is a chance (quite remote but still a chance) that the t-case sump is a little dry and howling. I believe that there are some parts in the t-case that rotate when the vehicle is not moving.

Good luck.

 

I wish it was that easy... The stupid shop that initally put on my cat-back destroyed my OEM muffler. Idiots!!! At this point, I'm actually considering paying $400 for another Ford OEM muffler just to see if it is infact the aftermarket system.



My truck is 2wd, but thanks for the suggestion.

 

Ok, so I just got back from local small muffler shop that specializes in hot rod and custom installs... They owner is a very nice guy. I described the problem I'm having, and was agreed to put the truck up on the rack to check out the exhaust system... He looked at it thoroughly, and said he couldn't see anything that would case this noise. Everything was installed & welded good. The only thing he could do was adjust the tension on all the hangers, in the hopes that it would stiffen the exhaust system... Other than that, he said everything looked good. He went over it for about 30 minutes, so I think he was thorough...

 

Did you notice this noise BEFORE you changed out the exhaust? Or have you made any other mods that might be accountable for the noise? I'd say it's in the exhaust system somewhere since with the engine in drive and the brakes applied the engine/drivetrain will "tighten up" and actually flex a bit...this could be causing one of the exhaust hangers to move just enough to vibrate against something......do you have the factory tow option and are you running your exhaust dual under the rear bumper....if so the passenger side exhaust where it goes around the rear tire/ tow frame assembly is a very tight fit and it could be moving and touching the tow brace - causing vibration....also, are your engine (motor) mounts nice and tight?

I had a 2001 Lincoln LS V8 Sport that did the same thing after I installed a Magnaflow cat back system....it would "hum" a bit at idle in gear with the brakes applied....it was only on an intermittent basis and since nothing was actually rubbing in the exhaust system - I just forgot about it - never caused any problems - but was most likely either a vibration being transferred through a hanger or exhaust shield that was too close or a resonance from that particular exhaust system that caused it - good luck.