The A/C compressor on my 1998 Bonneville sometimes makes a metallic rattling sound when the compressor clutch engages. The system cools as expected; the rattling sound is intermittent, i.e. is not always present when the compressor is engaged.

Here is a writeup from Dan Thurs that may be a match to address your compressor noise:

https://www.gmforum.com/mechanical-134/adjust-ac-clutch-plate-278951/