Noisy Lexus es300

I have a 1992 (or 93) Lexus es300 with 175,000 miles. It is making lots of high pitched engine noise and running rough. One shop replaced the power stearing pump, another replaced the rack and pinion. It still is making awful noises. Could it be the exhaust manifold or is somthing else going on

Under what conditions is it making the noise? Rolling? Turning? Braking? Only when the AC is on? Only when hot? Only when cold?