Noice on engine
 

My GF has a 00 beetle. For the past week or so every time she turns on the car you can hear a radiling noice on the engine for a few minutes. After that it goes away but it turns on when you turn on the A/C. It wont turn on if the A/C isint on, but after a 40min of driving i wont matter if the A/C is on or off the noice will start again. What do u think it is?
thanks for the help

I would guess it's the A/C compressor.