When driving, a loud continuous screeching noise comes from the rear left wheel area .... only 22K miles on vehicle. Any ideas?

- could it be brakes?
- was rear-ended a couple of months ago, could some problem from then cause this?

I have a 98 Zr2, same problem, checked breaks, nothing... Would like to know what it might be. it's coming from left rear. gets louder at different times..., when i hit breaks, it stops, maybe warped rear disk? any help is great! thanks all! ;)