Hi on our 5J Fabia 1.4 mpi,  when aircon is in use it makes a whirring sound which seems to increase in speed / loudness in sync with engine speed.

the aircon itself works fine and gives good cold air.

any clues on cause / solution welcome please 

Thanks

Had this sort of noise from our 1.9tdi  and it turned out to be the clutch pulley on the air con unit worn and dried out, turn it off no noise turn air con on squealing noise, had the pulley replaced by a local reliable garage who did the job in a day and was £120 all in parts alone were £73, now runs quiet