Sound is fine, then trickles dead

I have the strangest problem (very recent Samsung Smart TV and X1 service). When I power on, the sound is fine. But after two or three minutes, the sound dies -- and by that I mean, it kind of trickles off --  it's not a clean cutoff. It's like a circuit dying or something. But then next time when I power on, it's fine.

So, my TV is unwatchable. I'm interested whether anybody has seen this problem. I'll post on Samsung forum too in case it's a TV issue.