Hi Guys, hoping someone can help. Yesterday, went for a drive and as the weather was quite hot, I put the AC on but noticed that as I revved the engine, I could hear a distinct whining noise which got worse with higher revs. The air was still coming out cold but the noise is worrying me and it definitely was not there before. Can anyone tell me what the problem could be and roughly how much it would cost to fix. There are no fault codes etc as I have already checked. The car is an MK5 1.9 CDTI 05 plate.