My car as well makes a rattle noise with the clutch pedal out. When I press it in its fine, so I guess its the tranny. New T.O. bearing, new pilot bearing.

I also have solid motor tranny mounts. I get a horrible vibration/ rattle at 3.1k to 3.3k in 4th gear only. What would cause that its in no other gear at any rpm.

Also I have Delrin rear diff mounts and its super solid but on a nasty 1 to 2nd shift I get a clunk in the rear. por que??

 

wow, this is very strange. I have an 86 n/a and it sounds exactly like your car! I hear a "whirring" sound with the clutch out, when I press it in it's fine. Been told it's prolly a bad pilot bearing, throwout bearing should be ok though, was replaced <10k ago. It also makes a horrible sound right around 3k and ONLY in 4th. I'm not kidding. And once I got a nasty clunk when I was pushing the car hard, shifting from 1st to 2nd. My car has derlin subframe mounts and solid motor, tranny and rear diff mounts. I've been driving it like this for some time now (knock on wood)

 

wow we have twins.

I am sure the pilot bearing is bad...I had to reuse the old one since the new one was damage upon install.

The 4th gear thing is sooo strange.....I hope someone else knows.