[Jagdpanzer]

Could be the thin washer in the throwout bearing which retains the bearing. With the clutch ingaged the washer might be coming in contact with the back side of of the spinning outer shell which is retained in the pressure plate spring fingers by the wire retainer. You can confirm next time you drive by putting you foot on the clutch peddle and apply enough force to take out the slack in the TB without fully disingauging the clutch. I tested this tonight by taking the TB I just remove from my car and chucked it up on the lathe and spun it up to 2000 rpm. When slack you could deffenently hear the sliding contact noise which went away when tension was applied. Hope this helps.