Eliminate hum with Cary 805AE amplifiers?

I recently took delivery of a pair of Cary 805Ae amplifiers. Although these amps sound fantastic, I've noticed an audible hum which I can't seem to eliminate. I've tried cheater plugs in several positions, changed ICs, and ran an extension cord to the other end of the room. Not having an alternate preamp, I can't determine if its the problem. Wondering if anyone owning these fine amps has had similar challenges with them?
Is the hum audible thru the speakers or do you hear the hum at the amp? Also do you have a dedicated AC line?
If the amp is humming, it could be from the transformer or it could be DC coming thru the power line.
I'm asking you to clarify so you'll get a proper diagnosis.