Sometimes during a clutch replacement, the clutch cover-to-flywheel bolts don't get torqued properly and start backing out. The symptoms are shifting difficulty due to incomplete clutch disengagement, noise or clicking when shifting, and vibration with light pedal pressure near the top of the pedal travel. There is a TSB on this, 93-1-12 which lists the symptoms and indicates that NEW bolts must be used (part # N806606-S100, 6 required) and the bolts must be Loctited and properly stage-torqued per the shop manual.