[Mike Simard]

Hmm..Is the noise only there when there is some kind of load? If something in the clutch were looseining I suppose it could be held quite when there was a load present. Just a random guess. if you have the tunnel off why don't you rig up a stethescope to track it down. A big screwdriver with the handle held to your eear and the blade touched to the car works in a pinch.