Back before they had the wider neutral prong, present now even on two-wire plugs, common practice was to reverse the plug and leave it where it resulted in lowest noise. If you can try that on the receiver, it might help.
As far as I know, transformers such as the one inside the Denon do not designate one of the primary leads as neutral and the other as hot, so it is somewhat arbitrary in how they are hooked up. At least in the transformer wiring diagrams I have seen, one side isn't designated as Hot, etc. (Of course, if this is wrong, someone please correct me ).