Amplifier Hum

Hi, I have a Parasound HCA 2200 II that has started to make a humming noise. The noise is coming from the amp itself not the speakers. It just started doing this but still seems to function fine. Previously it was dead silent. The amp has about 3 years of use on it. My question: Is it time to sent to Parasound for a tune-up or is there somthing I can check myself? (the amp is not under warranty as I'm not the original owner) Any help would be greatly appreciated.
Thanks