1999 Oldsmobile Bravada STEERING TURNING

When turning into parking spots or making U-Turns I get a chattering in the turnig as if the wheels are locking up. Sometimes nothing happens but 'd say 80% it does. Any suggestions, before I have it repaired?

I've put about $2500 dollars in prior repairs. None in the steering or suspension. A rebuilt Transmission and (2) A/C repairs.

Thanks