[Razorback1980]

It could be a bearing in the transmission, however I am suspecting it's what I always called the throw out bearing. That's the bearing that rides on the pressure plate to disengage the clutch. Sometimes when they get a little older they make a noise when the clutch is out as they are not under load. When you push the clutch in, the bearing is pressed against the pressure plate and therefore under load and the noise stops. I am thinking the best way to tell is to determine if the noise is actually coming from the back of the car or just past the back of the motor. Put it up on stands and let it idle in nuetral with the clutch out and check out where the noise is coming from. There might be a better diagnostic procedure, I just can't think of it at the moment...maybe someone else has a better procedure.