yesterday afternoon, after my '03 ZHP with 60k was warmed up and sitting in the garage, i started it up. when i shifted into neutral and took my foot off the clutch, i heard a knocking noise coming from underneath the car, roughly the transmission area...the knocking was periodic, about every half-second. "felt" like some mass was loose and rotating in the bell housing if i had to guess.

i didn't rev the engine to see if it was RPM dependent (wasn't thinking at the time), but when i pressed the clutch in, the knocking noise went away. took foot off, knocking noise came back. i shifted into reverse and let the clutch out, no knocking noise.

something going south in my clutch? cars shifts and drives fine, and i don't get a knocking noise while driving around. i'm easy on my clutch, tho i do not drive the ZHP on the track, i do heel-toe, but that helps with rev-matching on the downshifts. throw-out bearing going bad? unbalanced flywheel? thanks in advance for any help given!