A/C Compressor knocking

Thanks for the quick response guys. The car is at a shop and they did the entire install. The original compressor was shot so I went to advanced and got a stock replacement (2 piston I believe). They completely flushed the system, new condenser, new dryer, new control unit and new under dash vent set up.

When I took the car for a test drive today the a/c blew ice cold. Only downside was that knocking sound. They said it could be cause the compressors so new. Could be a case where it needs to break in? I honestly have no idea. I've never had an a/c work on either of my A bodies.

I later found out about the newer style sanded units. Wish I had known before to having the shop do all the new lines for the older style compressor.

Heck maybe its a bad core?