I have a 42" LG plasma. Love it and the only problem I have (that I probably caused by accident) is the speakers make a little bit of a humming noise every once in a while (when the right tone is produced) because I think one has a little tear in. I had a 32", a 50" and this 42" flat screen TV, and I didnt need 3 so I put the 42" in storage. I have since sold my 32", so I figured I would pull my 42" out of storage to use in my room (like the 32" was). I think since it was sitting in storage and it was a little humid, this weakened the paper in one of the speakers (absorbed the humidity) and caused a slight tear when I started using it again and cranked the volume up. My slight buzzing noise every now and then is probably different than yours though...and mine is a simple fix as I just hooked my receiver up to it and turned the TV speakers off...
Use some percussive maintenance maybe? (hit it)
j/k... I would probably exchange it, but since you bought it online, that always makes it a little tougher since you have to ship it back and wait. This is especially a bummer around x-mas time since it will probably make things take even longer (or you will probably wait until after the holidays to do it...).
Small graphics glitches when game systems are starting up/shutting down is one thing (like one CAG was recently complaining of)...but hearing a constant buzzing sound is another. That is never a good sign and I would probably lean toward the idea that something is wrong with it. I would exchange it before it breaks.
Could be a plug. Hopefully on the end of a cable and not the TV itself. I had an S-Video input that buzzed like crazy. I'm thinking because of the weight of the cable kinda warping it over the years. I blame those stupid "dongles" in the middle of the cord, like you'd find on a VGA cable. That's pretty much why they came out with those "cable savers" to suspend the cable instead of having it hang with dead weight.
