I have a 95 LT1, and there is a clunk (sounds sort of like steel on steel) when I shift to drive or reverse. Sometimes it's 2 or 3 clunks. It drive fine, but just clunks when going into gear.

U-joints are a common cause of clunking when going into gear, so I'd check.  Also, how's your tranny fluid?  Is it low or need to be changed?

Could be u-joints on either the driveshaft OR the halfshafts....or all of the above. Could also be loose hub bearings, or worn bushings in the rear suspension.

The "creaking" "click" can be cured with a $7 Teflon washer between the rear spindle and bearing. I fought this noise in my 88 for 3 years, and never fixed it before selling the car. My 85 is beginning to do it. I found a thread on CF with about 50 "this worked for me" replies regarding this washer, and the GM P/N for it. someday I'll get around to searching for the thread again, and installing the washers. Or then again, maybe not, because it causes no harm.

A worn u-joint usually "rings" the hollow drive shaft when it clangs. Very distinct bell-like sound.