What engine do you have?

It may not be compressor noise that you are experiencing. It may be a worn drive belt, belt tensioner of belt tensioner shock which will all make noise when the a/c is on at idle.

To drain the oil out of the compressor would require the removal of the compressor or a comprehensive flush of the system with nitrogen. As long as you don't have a leak, I wouldn't worry about it.

__________________
Alex.

MB Tech
Sydney, Australia
Volvo 122S
W201 190D 2.5 manual
W202 C240
W203 C32