Thanks to everyone for their input.
Originally Posted by chunon
Wonder if it has something to do with the set expanidng or contracting because of heat ?
This is exactly what Panny first tried to tell me was my problem. I didn't buy that for me, but it may apply to you. Or not.
In any case, my update is that I contacted them over chat. They came back with other inane things (unplug the HDMI cable; did it happen again?) until I asked what part on the TV makes that noise normally. When she wrote, "I don't have the information on the inner part, who will have this information would be our technicians", I asked to be connected with one. So their Concierge will be contacting me to talk with a tech. I had brought up the buzzing in the chat, as well.
@aidoroboo: For all I knew it was HD-nirvana coming in and crap coming out only due to the TV, so I'm relieved to hear it's much more likely the crap was something else. Score a learning for me.
Also, I had picked up a Wii component cable when I first got the TV: $5.59 from Amazon back in late March (now $3.94 from Amazon, and looks like $3.92 from MP, oh well). So now I have 480p there. Thanks for the tip b/c I could have missed that one.
Monoprice: I've read (here/elsewhere) and browsed them before, but I guess I just haven't gotten used to their interface to buy anything from them. On the one hand, it's overwhelming (so many choices, bad layout for me, my brain shuts down), and nothing is rated which I depend on Amazon for (I guess that's a trust issue b/c I'm unfamiliar with the seller/product ... should I trust everything they sell?).