When I turn it up, it turns down

Take the advice you see above. This just happened to me with a Music Hall Maven that I use in a room just for TV sound. I was planning to give it to Goodwill, but just for fun I plugged it back in, and guess what? It worked fine!

I would email the NAD North American Distributor. Send a very detailed description of everything involved with what is happening when the M3 does this. Ask NAD if they have any feedback/suggestions. If you ultimately need to have the M3 serviced to solve this issue, NAD has authorized service centers they can refer you to. Keep the NAD North American distributor aware of every step you take. NAD can be very helpful in these situations.

The above recommendation is if you can't fix the issue with the suggestions given to you in this thread. If any of your fixes don't work out, I would contact the authorized NAD service center recommended by the NAD Distributor, let them diagnose the problem, and then email the details of the repair and cost to the NAD Distributor to get feedback.