Buzz at 2K RPM

[0xfded]

I had this exact same issue on my '91 pickup (manual), and am having it again on my '98 4runner (manual), so I was wondering if anyone else has noticed this (and diagnosed it):

Right around 2000-2100 RPM, something metallic resonates on the undercarriage, apparently forward of the transmission. It only seems to depend on engine RPM, not speed or gear.

It sounds like thin metal, a grating or something. It buzzes in that range, and then is gone outside of that range. No big deal, except that you pass through that range every time you shift. Drives me nuts.

My suspicion at the moment is the skid plate, but I haven't pinned it down yet. Before I climb under there with the engine going at 2k, has anyone else diagnosed this before?

 

[curtperry]

have someone rev the engine while you lay underneath.

 

[0xfded]

have someone rev the engine while you lay underneath.

Yeah, I expect that's probably in my near future. That or fixing a pair of vise grips to things that might be vibrating and revving it myself.

 

[98OzarksRunner]

This: http://www.toyota-4runner.org/3rd-gen-t4rs/138032-rattling-sound-only-when-accelerating.html

If you figure it out let us all know.

 

[0xfded]

This: http://www.toyota-4runner.org/3rd-gen-t4rs/138032-rattling-sound-only-when-accelerating.html

If you figure it out let us all know.

Yes, that thread lead directly to the culprit, the exhaust heat shields. I pulled out the rear one and went for a spin.

75% of the sound gone, and I'm certain the other 25% is from the front shield.

So now I have to figure out how to sound deaden those two things. Going to try pulling off the front plate and having a closer look at where they contact tomorrow. It may be that some spacers might do the trick.

 

[opie74]

They start to rattle when the spot welds holding them on, break.

 

[0xfded]

They start to rattle when the spot welds holding them on, break.

Didn't see any broken welds on the rear one (it was held on by two bolts, no rust anywhere), but I'll have a look for them. Those would be obvious noisemakers.

Have a roll of high temp silicone foam tape coming in my next batch of goodies, so that should take care of things if I can pin down the trouble spots.

 

[masphx]

My sounds is coming from something different. It only does it under load around 2000K and 2500K. I can really hear it when the Rig is warming up. After warm up I can still barely hear the sound.

I have tried to figure out what this is for the last two years. I have...

-Replaced transmission mount
-had a shop spot weld those heat shields
-hit everything with a rubber mallet underneath

The one thing that does 'rattle' is the catalytic converter but only if I hit it just right. The shield around it seems fine. Sounds like a rattle from inside. If it is the Cat don't understand why it only makes the sound under load at 2000 and 2500 rpm.

 

[4yotaguy]

My sounds is coming from something different. It only does it under load around 2000K and 2500K. I can really hear it when the Rig is warming up. After warm up I can still barely hear the sound.

I have tried to figure out what this is for the last two years. I have...

-Replaced transmission mount
-had a shop spot weld those heat shields
-hit everything with a rubber mallet underneath

The one thing that does 'rattle' is the catalytic converter but only if I hit it just right. The shield around it seems fine. Sounds like a rattle from inside. If it is the Cat don't understand why it only makes the sound under load at 2000 and 2500 rpm.

My old manual did this too and it was a worn T/O bearing,,,not that it was bad, just made what may be a similar noise to yours after I replaced the clutch and flywheel....

 

[masphx]

My old manual did this too and it was a worn T/O bearing,,,not that it was bad, just made what may be a similar noise to yours after I replaced the clutch and flywheel....

Interesting, how would I know it is a worn T/O (don't even know what that is)? Can you go into more detail? Original owner said clutch was original and I picked it up at 168K. It now has 192K and clutch is still strong.

Here is a video of my sound I made a year ago...

https://www.youtube.com/watch?v=A9i8EYTsRrM