why does my clutch vibrate

every time i hit the clutch when im around 4000 rpm or higher in my 98 lude the clutch petal vibrates intencely sdoes ne one kno why

your clutch cover may not be balanced.. the clutch-cover to flywheel bolts may not be properly torqued, and are starting to back out..

Just a Q for Black 98, when your in 3rd gear and you floor it, does your stick vibrate at all?