My Pioneer receiver has a humming sound that sounds like a cooling fan, but it cuts in and out. Is there a fan in the receiver and would it keep turning on and off as if connected to a thermostat? It is very quiet but if you put your ear close to the receiver you can hear it go on and off. If this is normal I will not worry about it. However, to remove it from its current location is a major operation so do not want to do it unless this is indicative of a problem and not normal.