Checking the power steering belt adjustment is a good first step. That's the most likely cause of noise.

Flushing the system and refilling it with synthetic ATF is a good idea too.

Check the alignment of the power steering pulley to the main crank pulley-- is it running straight? If not, suspect the power steering mounting bracket.

Take the belt off the power steering pump and check for play by wobbling the pulley. Inspect it for leaks-- if the seal is shot it will be wet underneath. I just did a replacement of the power steering pump on my '92 945T and was surprised how inexpensive the pump was.

I've seen steering racks that were still tight but that lacked assist because the internal seals were shot. Usually when the steering is sloppy it either inner or outer tie rod ends, or the lower steering u-joint that's bad.

Jack the front end up and check out the front end for free play. You may have several things that need attention.

Good luck!