engine and drivetrain Update on mystery noise

[Columbo]

I wrote a while back about a couple odd sounds I was trying to ID.

 

I recently found some time to investigate a little further and here is a few new clues:

 

I put the car on jack stands and fired it up.  After triple checking the stability of the car, I got in put it in first and slowly let the clutch out.  I did not hear the Shhhhhh sound.  Second gear I heard it, third it was louder and fourth its a very loud SHHHHHHHHH sound.

 

This has really got me baffled, please help.

[Russell74Fjord]

hmmm, considering what you are describing, check those things that rotate faster, as you change gears, since the noise gets louder, so driveshaft, guibo, universal joint, CV joints,

 

With the car stopped, cooled down, get under there, grab the driveshaft and see how much play there is, inspect each universal joint, there should be no play at all. At the transmission end, inspect the guibo, there should be no cracks, or looseness, sometime the cracks can be hard to see, so really pull on it, I doubt you can break it, or do any damage. Check all other connections, gear shift, cross member, exhaust, While up in the air, check wheel bearings, also should be no play, and spin freely.

[Columbo]

The driveshaft has no play (other that about an 1/8" rotational), the guibo looks new and so do the bolts.  There is also a new rubber bushing above the gumbo.  The wheels spin freely.  There is some grease around the cv joints but unless they were bone dry (which they are not) I cannot imagine they would be making such a high pitch "shhhhhh" sound.

 

I have a strange question.  Is the amount of exhaust (pressure and/or volume) the same at 3000 rpm in 1st gear as it is at 3000 rpm in forth gear?  I'm beginning to wonder if it's an exhaust leak that I'm only hearing at higher pressures, i.e. 2nd, 3rd, and 4th gears.  From the headers back, it's an old exhaust system.

 

Thank you for helping and please keep the suggestions coming.

[69NEWCLASSNH]

sounds like a throwout bearing..

 

[Simeon]

Put a cloth over the exhaust pipe with your hand to block it and listen with your head underneath. That will show you any exhaust leaks. 

 

Be be aware that running on axle stands is not an exact simulation of what happens on the road. Without the load on the drivetrain you are not stressing the components exactly the same. 

[im3crazy]

+1 throwout bearing

[TobyB]

I have done this, but be VERY careful if you choose to-

 

I've rolled under the car with it running to figure out where the noise is coming from.

It's terrifying seeing all that spinning stuff under there.  Then rigged a wire to let

me rev the engine while I watched things spin.  I did make sure I had the rev limiter

set to a safe limit...  

 

It's also very educational when you have an unbalanced driveshaft- and even more terrifying!!!
 

 

Your noise makes me think differential.  But then, that's just over the internet...

 

t

 

[Columbo]

Tony, you are more brave than I am!

 

Anyhow, the noise isn't there if I just rev the engine, only when in 2nd, 3rd ,and 4th gear with the clutch engaged. 

[Hans]

what about the center bearing?