1995 Buick Riviera supercharger

If it's rattling it may be worn out. It not a serviceable part meaning you have to get the whole thing. However check the belt and tensioner it may be a bad tensioner making the noise so replace both.

GM vehicles equipped with superchargers.
Premature failure of supercharger bearings.
When the belt tensioner starts to fail, belt tension increases dramatically. This tension shows up as side-loading in the supercharger rear bearing.
Periodic inspection of the belt tensioner should be part of the regular maintenance routine. Before operating the replacement supercharger, the tensioner must be inspected and replaced if defective. Unless the tensioner is checked and replaced as needed, supercharger-bearing failure will occur, causing premature catastrophic failure.
While this problem is prevalent on GM vehicles, this inspection should be performed on all belt-driven supercharged vehicles. Please check your vehicle service manual for the recommended inspection and service.