Get a bit closer to the problem, crouch in front of the grill and get someone (that you trust implicitly) to operate the aircon, listen for any unusal noise from the fan, same again with the bonnet open. See if you can locate it that way.madone said:It could be gurgling but not sure. Something "kicks in" and then goes off causing the tickover to vary. Picked up my daughter tonight and its the first time she has heard it. The air con appears to work ok but for this problem.