I just installed my new system including a Harman Kardon AVR 445 receiver and when the receiver is in use for a certain time (15 to 30 minutes) I begin to get an intermitent noise coming from the receiver itself.
It lasts about 2 minutes, then stops, then begin again a few minutes later, etc..
You'd have to ask either the dealer or HK whether it is "normal". If all is as should be, there isn't any reason to lower the volume of the fan as that would lower the benefit of the fan.