I have the exact same behavier with my S80 V8 from '09 here in Germany. It makes this noise from the A/C since 70.000km/45.000miles respectivily 5 years. The A/C works fines. The noise goes away after 30 to 60sec. It just appears after driving around, park the car for a few minutes or 1/2 houre and then starts the car again.