I found this at the review below, maybe you can save the Parasound.
[May 17, 2007]greasemonkeyAudioPhile
The amp delivers a powerful and clear sound. It is only seconded only by my favorite amp the BA-5000 from Sansui. Great design carried out with quality components.WEAKNESS:
The initial hum caused by a floating ground condition.
I picked up a HCA-2200 II from ebay a few years ago. I also had the same problem with a 60 cycle hum which came out of one channel only. I decided to explore the problem internally after trying the ungrounded plug adaptor trick which only minimized the hum slightly. What I found was that almost every screw either internally but especially externally in the case was loose. They were loose enough that you could turn them by hand. So, I checked each fastener and tightened down every loose one. That one thing eliminated the hum completely. I could only guess that the problem was from a floating ground condition. I can only surmise that the fasteners were not torqued down to a reasonable amount during assembly at the factory and over the years they continued to back out by themselves due to vibration.