Identify that noise

[imag]

I have a noise I am trying to figure out. Unfortunately, I can only hear it at higher RPMs when the car is under load, so I cannot localize it or get a decent audio file of it. Here is my best description:

- It is a rotational metallic whirring sound. It is not louder than the engine, but it is loud enough that I am worried about a worn bearing or something similar that might suddenly go up in smoke. It is not shrieking or agonizing, just whirring.

- It only occurs on throttle when the engine is under load; If I back off the throttle even slightly, it stops instantly.

- It is definitely engine RPM dependent, not wheel RPM dependent, so it must be forward of the driveshaft.

- More load seems to slightly increase the sound, so I hear it more in fourth or fifth gear on the highway than at low speed.

- It is hard to discern sounds in my car, since it is a collection of sounds and rattles, but it seems to only start manifesting around 3K RPM or so. It is most obvious cruising at over 3000 RPM in 4th or 5th gear. The pitch of the sound is not high, not low - it sounds like a part that is rotating about the speed of the engine - 3K-5K RPM.

- I noticed it after coming home from a driving weekend that included a track day as well as dirt road driving with lots of dust. So it might have resulted from high RPM or lots of dust/vibration.


My two hypotheses:

- An idler or other gear in the transmission is worn.

- The alternator bearing(s) is/are worn, and it only makes noise when there is belt tension and speed

I thought you all might have experienced something similar and know what it could be. It's pretty difficult to poke my ear around under the hood at 60 mph.

[mraitch]

Well, you can rule out the alternator by buying a shorter fan belt and bypassing the alternator while keeping the water pump in action.

Is the noise occurring ONLY when in gear - you have coasted at high speed I presume.

[jrusso07]

Counter shaft gear is a good guess

[redroadster]

Those electronic stethascopes were pretty afordable the last time i checked . Well $70 -80
and very handy for this type of thing plus you can be the guy in your neighborhood that diagnoses hard to find noises then.
bell housing bolts tight and alignment dowl rods in ? no rusted U joimt caps ?

[imag]

Well, you can rule out the alternator by buying a shorter fan belt and bypassing the alternator while keeping the water pump in action.

Is the noise occurring ONLY when in gear - you have coasted at high speed I presume.

Great ideas folks. I need to check coasting at high speed *with* the engine at 3K+ RPM.

And the electronic stethoscope is really interesting. That could be handy for all kinds of things! Will keep you posted.

[dbrick]

Have you checked the trans fluid level? Counter gear is a pretty good guess, it's the only thing in the transmission that always rotates in relation to engine speed. Might be louder if you get up above the range of the noise in gear and lift off the gas, letting the engine brake the car.

[bchen]

Apologies for bringing back a 9-year old thread, but I’m having the same problem, except that mine is 4 speed and the sound happens towards the top of 3rd and most of 4th. Like imag, the sound is only present when I’m applying power. As soon as I let off the accelerator, the whining sound goes away.

Also, I just replaced the axel bearings, so it’s probably not coming from those. I’ll take a look at the counter shaft gear.

@imag if you’re still around, did you ever identify the source of this problem?

[jrusso07]

On the 4 speed, the counter shaft where it rides in the transmission case tends to ware and the whole shaft can move in and to and from the gear train.

You can pull the bottom pan and grab it and see if it moves.

[david premo]

It could be the ring and pinyon going bad. Ring and pinyon are bad in either acceleration or deceleration and that is what I would be looking at. When you hear noises both ways that’s typically axel bearings going bad. Typically for the transmission the counter shaft in the transmission is noisy on deceleration when the shaft moves and it contacts the output shaft gears, I not sure I have seen one that was doing it under acceleration.
Dave

[redroadster]

All above......, are the Trans to engine block bolts tight and present , I worked at a import shop , I pulled 4 or 5 Trans in the 9 months I worked there , ( every nearby parts store clerk cussed at our owners name) that the aligning sleeves or pins were missing and / or bolts loose & caused a whining noise