I think if he had a ground circuit loop, he would know it because he would have fantastic hum, but maybe not.http://www.smr-home-theatre.org/Ground-Loops/
So you need to look into it. The easiest way is by using an extension cord to plug into a different circuit. Or the same circuit if he already on two different ones.
But I suspect that surges are periodically happening in the DVD player.
Intermittent things drive me absolutely crazy. What I would do is to rent or borrow a different DVD player, plug it in and see what happens after a few weeks (and play every DVD he can get his hands on). If nothing bad happens, we know where to point the finger.
That's about all I can suggest. You need to get off-center, off the dime, whatever. Three boards should be screaming something is bad wrong.
I ain't no electrician, but I sure had to learn their job when the dopes around here kept screwing things up. We used to go 'round and 'round, for hours. Things have gotten much better since the State began requiring Continuing Education. I can imagine their faces when they were sitting in class hearing the same things I had been telling them for years.
Now when I tell them I want an isolated circuit and a separate, but bonded ground not hooked into the neutral, they shut up and say "Yes, sir." And if they they think they can fool me, I have a $500 Sure-Shot tester, just to make sure.