Problem solved. Don't neglect your connections.
Posted by: winkyincanada on 23 April 2017
Yesterday, an intermittent scratchy/static/rumble sound started to come from my speakers. Just for a second-or two, every few minutes. Interestingly, it occurred even with my SuperNait muted. I tried unplugging and replugging the speakers. No help. I then gently moved the Snaics at the back of my HC. The noise was directly correlated. I unplugged and replugged and the noise is gone.
There is lots of previous advice to periodically perform an unplug and replug of all connections from a SQ perspective. The wisdom of that advice is now apparent to me.