89gtwith3.55s

i had the same problem, and like everyone is saying its the throwout bearing... my problem was that i had a cheap clutch fork and it eventually wore away at the TO bearing... check it out... could be your input shaft too

1FINE99

I would guess the TO as well is chattering on the input shaft and you can grease it to make it quiet down but that is usually a temp fix since the grease will eventually go away and it'll come back. I had a similar prob. as well and polished up the shaft with emery cloth and it went away.