Right Channel Cuts Out intermittently - help!

Hi all,
The right channel in my system cuts out intermittently, no matter what source I’m using. I’ll be listening to whatever, then suddenly I hear a static windy sound from the right channel, and then it cuts out. Then, it comes back, but not for long.
I hooked up a different speaker to that channel and the problem persisted. So, it’s not the speaker. And, as I already stated, it’s not the source components either.
I can’t afford expensive cables - I’m using heavy gauge speaker wire. There are no faults that I can detect in the wire.
Currently, I’m using a HK 4390 Receiver as a preamp/control unit, with a parasound a21 amp. I switched the ends of pre out cable, but the problem remained in the right channel. I also swapped it out with a new cable, which made no difference. The a21 is only a year old, and it is my understanding their build quality is superlative. This problem only started a couple days ago, and I’ve owned the a21 for about a month. It seems unlikely that it is the culprit.
I’m thinking it may be the pre out on the HK.
However, here’s the strangest bit: I disconnected the pre out cable from only the right channel on the a21. With no input from the HK, the static returned again in the right speaker for a brief moment. When I reconnected it, nothing changed. The channel still gets bouts of static, then cuts out.
This is driving me nuts. Could be a power cord or grounding issue? Any help would be greatly appreciated.