When does the sound occur?

stock clutch/pressure plate/flywheel?

take care,
ChrisS

PS,
Stuff to replace when doing the clutch: (in the long run these will save you time, labor, and headaches)
-pilot bearing in flywheel
-clutch
-pressure plate
-throw out bearing
-resurface flywheel (or swap for remanufactured flywheel)
-rear main seal on engine