Hi,

It's hard to judge these kinds of problems (strange noise problems) from behind a computer...

I assume the noise is coming from the compressor element itself? Is it a metal type sound?

I'm afraid I have some bad news. I suspect your compressor element (also caled air-end) is ready for replacement. Probably a bearing failure. Probably better to not use the compressor anymore until the problem has been resolved. If it's just the bearing now, that's relatively cheap. If the rotors get damaged, that's a lot more expensive.

I suggest to call Atlas Copco to come check the problem. They can repair the compressor element or replace it with another (re-conditioned) one.

How many running hours does the compressor have?

Please let me know how it works out..

Good luck