If your car has a/c it is normal.If your other car had no refridgerant or had no a/c installed may be a reseans why you didnt hear it.In defog and mix position the a/c compressor cycles for a few reasons such as keeping the system operational,cooling the cabin, and to aid with the defoger if needed.

__________________
Nicks Automotive
2334 Wyecroft rd unit 2
Oakville Ontario
L6L 6M7
www.nicksautomotive.ca