Probably just a dumb volvo newbie question...

my 2002 s80 t6, when idling, makes a clicking noise underneath the hood. Just a single click every once in a while, and the engine seems to change speed (haven't looked at the rpms when it does this) Is this normal?

 

Off the top of my head this could be one of two things.....not just for Volvos.
1. A/C compressor
2. Cooling fan

I'm sure the experts here will chime in with more.