My guess is that you are hearing one of the TV's cooling fans. It is summer now and maybe your house is warmer than it was a few months ago.

Just to be sure, what is the model number of your Panasonic TV?

Thanks. Model TH-42PX600U. A cooling fan was not even considered. It makes sense that a large plasma TV might have one, or two. Sure makes better sense than me thinking it might have a hard drive. They really do get hot, don't they. About a year ago I bought a 5 speaker Samsung DVD system. I left the TV on when installing (probably wrong) and really could feel the heat. Thanks again. Gene

If it's definitely plasma, I'd guess fans. If it's a DLP then it could be the mirror thing spinning.

Yup. It's a fan. No hard drive in that TV.

DLP would be a color wheel on a non LED model.