Noise when turning...
'99 z28 with 56k miles
Squeak from rear on sharp turns: If it makes the scraping/screeching sound on hard turns, this is your most likely problem. It's just a matter of shimming your caliper out, that’s all, and would take about 30 minutes to repair. The sound you're hearing would be the caliper itself hitting the rotor on the turns. One quick test for you to do is to go into a parking lot and go into the hard turn, once you hear the scrape, apply your brakes. If the sound stops, then its even more likely your caliper's hitting. What your doing is pulling the pads inward thus your calipers won't hit.
This is a fairly common problem with our cars since the specs are so small of a range...measurements are 68.625-69.79mm (2.70"-2.74") from the inside caliper mounting bracket to the outside face of where the stud bolts mount to. The shim btw is part # 26034667 If your rotor is out of spec on run out then your problem can be worse.
Or here is other dianostics for other problems
http://www.go-fast.org/z28/diagnostics.html
Justin
On a sidenote, I never had this problem until I ground down my calipers to fit some prostar 15X10's on the other day to go to the track. Now mine does it as well. 

