Volvo Repair: Air Conditioning Noise, volvo xc 70, engine roar

Question
Regis, I did have the freon checked last week and my mechanic said it was fine (they did top off with .75 grams.  It is still making the clicking noise which is accompanied by a noticable engine roar as if the compressor is kicking on and off.  Could it be a compressor problem or is this normal for the XC?
-------------------------
Followup To
Question -
1999 Volvo XC 70
When running my AC I hear a very clear and noticable "click" or "tick" noise approximately every 10-12 seconds coming from the dash area (sounds like middle to passanger side of dash).  The AC is running cold and I have had the coolant checked and it is full.  This happens regardless of whether I have on "AC" or "Auto" with the AC engaged.  It does not happen when the AC is off and the fan is running.  Can you provide some insight?  Thanks in advance for your assistance.
Answer -
this is the air conditioner relay switching on and off.this may be because the system is low on freon.it will need to be checked to have the pressures checkf to see if it is low on freon.

Answer
the compressor will cycle based on freon pressure.when it goes so low it shuts off.it may shut off due to high pressure also.the pressure would need to be checked at the time it cycles on and off.some cycling may be normal but it should not due it frequently.unless you have the fan on speed 1 and are on the highway.