Power steering/alternator connections rattling

[CaptainYeroc]

I have a 1987 Porsche 944 and it just started rattling loudly. I looked under the hood and I noticed that the power steering belt was looser than usual. This seems to be because the circular part connected to the engine block is loose (I can wiggle it around with my hand). Right next to it, the other circular part connected to the engine block that attaches the alternator belt might be vibrating...it's hard to tell.
What are these parts attached to the engine block?
How can they be tightened or replaced?
Anything else that could help would be much appreciated!!!!