I should be clear, it sounds like a buzz if I put my ear on the unit. The sound is obviously a vibration through the casing. With my ear right above it, it sounds like a quiet operating fan like you would hear in a PC, not a buzz. I just never heard sound from a receiver before, and that's why I was concerned. I don't think it's a malfunction, just a normal operating feature of a high-wattage receiver. The fact that I heard it on two units and others are hearing the same fan noise, I am not concerned.