Yes, DEN to IAD was A B777 - the audio was out for my seat and my seatmate's seat - but worked everytwhere else. It wasn't a headphone problem.

Yes, I reported it all 3 times, very nicely. And, no, I won't write UAL or make a fuss. They have enough problems.

I will assume that being 3 out of 3 flights with these issues so far this year is a fluke. The good news for UAL was that all 3 flights were 100% full.