Its the clicking when the AC is on that's pushes me towards it being the AC its self, and bad bearings can be audible if the cage is thinning out or coming apart. It is possible that it is the compresser clutch making the noise, but I'm hoping the OP knows what the clutch sounds like normally.
TO the OP, DO NOT take a single answer as being the end of this thread. Mine post is what comes to my mind, whynotthinkwhynot has other ideas, which can be more easily checked. Look at all possibilities that you can fix on your own first.