New Buzz/Resonace Sound - Diagnosis Help/Confirmation

Approximately one week ago I noticed a new sound resonating from my truck. I can best describe it as a drone/rythmic buzz that has a deep pitch. It sounds almost like a muffled brass instrument. I visited a dealer last night and my gut questions their diagnosis, so I'm looking for some second opinions.

I have so far been able to determine the following.

1) Noise is more prevanlent when the engine is cold. As the engine warms to operating temperature the noise subsides in volume and frequency of occurance but is not eliminated.

2) Noise appears mostly under low throttle and/or RPM range. Especially when backing off the throttle.

3) Noise appears to eminate from the engine bay on the passanger side.

4) Noise does not appear when the vehicle is stationary (as best I can tell).

5) Noise appears independent of road conditions and steerling wheel position.

6) No obvious signs of anything rubbing, parts disconected, damage etc.

7) Vehicle otherwise appears to run normally.

Visit to the dealer last evening resulted in a diagnosis of - Exhaust heat shield surrounding the catalytic converter is rattling, especially at cold temperatures.

Truck Facts - 2005 V6, 4x4, Automatic Transmission, 60,00x miles, stock tires, and vehicle is completely stock mechanically. I am the second owner and have had it for ~10 months. The 60,000 mile service was performed just prior to the noise appearing.

Thanks for the help in advance. Sorry for the long post, I wanted to provide some detail.
(Mods please move to 'Technical Chat' if you feel it is more suited for that sub-forum)

 

After dinner bump!

Note that the vehicle has been in 2WD.

 

Early Morning Bump.

Any help or theories would be greatly appreciated.

 

I'll venture a guess of a wheel bearing going. since you noted noise isn't while stationary and side specific. Were your tires rotated at service? Maybe a tire slightly out, or, a different wear pattern from being on the lighter rear? did you/they adjust pressures at rotation? I say check tires first, then wheel bearings. Good luck!

 

Noise go away when you put truck into 4hi?

 

The tires were rotated as part of the recent service. I havent noticed any uneven tire wear. I'll check for uneven inflation as well.

My biggest fear is the issue is transmission related due to the issue manifesting itself at a specific rpm / throttle position.

Thanks for your help!

 

I haven't tried putting it in 4wd. I can look into this as well.

Thank you!

 

Last minute suggestion bump. I will be going back to the dealer within the hour and will have them test the vehicle from a "cold" start.

Any more suggestions? Thanks again for the help.

 

I'm not sure. I have some vibrations and noises coming from mine also that I can't pinpoint.

Good luck with the dealer. In my experience they are as useless as an air conditioner in the Arctic. The only thing they're good at is taking money for faulty diagnoses.

 

Its probably just a sheild or somethin stupid, mines got alot of new buzzes with this cold weather, check/replace the foam around your intake at the fender for a start

 

Hopefully these technicians are slightly more useful

The vehicle is still under a factory warranty (certified used) so I might as well take advantage of it while I can.

 

Fold up small piece of cardboard, or foam, or anything that can fill the gap where the air intake goes into the right fender. Make sure that it is preventing the movement of the air intake hose going into the fender, or no more wiggle room for the intake/fender(will be ring of cheap foam in this area that is no longer preventing the buzz)
Should take less than a minute to fix.

 

what was done for the 60k service? Since the noise started to happen after the service, maybe they had forgotten to tighten something. It might just be a coincidence that it happen after the service, but I would look over the areas they had to go through to perform the service to make sure nothing is loose.

 

At the dealership now, noise was verified during my test drive with the technician (thank God). Technician's confused response upon hearing the noise was slightly amusing.

They have since retracted the rattling hear shield diagnosis.

I would have to see precisely what was included in the 60k service, my print-out is conveniently at home and I cannot recall everything the manual recommended.

I will suggest the techs look into the intake. I originally suspected that as well and found the foam ring in place and from what I can tell, functioning as designed. I am beginning to doubt the intake as the source of the noise as the sound emanates at specific rpms and or throttle positions.

Thanks for all the ideas everyone! Keep them coming.

 

Sounds almost exactly like what I was experiencing. All it takes is a bit of foam shoved into where the air intake hose meets the fender and it's problem solved. There was a TSB for this and Toyota redesigned this for newer Tacomas.

 

The foam insert between the intake and fender is preset. After the recent posts, I made sure the technician inspected it with me there.

Dealer is calling toyota tomorrow for instructions on how to proceed. Thanks again guys.

 

The foam ring WILL be present, but you need to wedge something in there to stop the play in the air intake hose. very simple fix if this is your problem, and it sounds like it is

 

Sorry, looks like I have misinterpreted what you and others were saying earlier. I will look into this further tomorrow morning.

 

I hope that is my noise too. Mine is a loud buzz you can hear and feel for a few seonds upon cold start, then quickly lessens to quiet; but the colder the weather is, the longer it buzzes. At 20F it will buzz for a few miles. Right side under hood, close to fire wall. By the time I drive to dealership, its warm and quiet. Gonna get me some cardboard tonight. ;-)

prs