Need Help With Diagnosing A Problem

I have a Peachtree Audio Grand Integrated X1 (Class D) amp.  Intermittently and spontaneously, while playing a source through the analog inputs, the volume will start "blaring" quite loudly and cannot be controlled, up or down, with the volume pot (which is a voltage-controlled amplifier gain control).  The only way to stop the blaring is to shut the unit off and let it sit for a while (perhaps draining some caps, I dunno).  The last time this happened, I shut the amp off, waited a little while, and turned it back on to find that I could force it to happen by rocking, off and on, the main power on/off switch on the rear panel.

I was stumped and sent the unit back to Peachtree Audio for evaluation and service (it is beyond the warranty period).  The amp has been on the tech's bench for over a week and they cannot induce the volume blaring issue. They say they have check some of the connections and such and have found nothing amiss; and they cannot diagnose the problem.

I know there is something wrong and I want to avoid getting it back, after the inconvenience and expense of packing and shipping it out, only to have it blare again once back home.  BTW,  I am using an older Luxman R115 receiver as a backup with the same sources, same interconnects, same cables and same speakers, with no blaring or other volume issues so it must be something with the Grand Int.

Any suggestions out there about what may be wrong or how to force it to happen (while Peachtree still has it)?  Please, no debate about whether Class D is worth owning.