1994 Audi 80 Popping noise becomes a bit louder with AC on

Hi, there is a quiet popping noise, you can rather hear it when you are inside, doors and windows closed engine at idle. When accelerating, the popping accelerates as well, to a certain extent, of course. Then the challenge is when you turn on the air condition the noise becomes louder, if the engine is at idle. The car has been looked at by a professional technician, he said the noise comes from inside the compressor, then why you can still hear the noise when the ac is off? There is nothing loose, the ac is operaring normally, but the popping is a bit louder than four months ago. All the belts were changed last week. It does not sound as cam followers, the noise is rather coming from underneath. Help please if you have any idea. Thanks.