Noise in speakers as people talk.

I purchased the TH42PZ80U on Nov 29, 2008. Found settings for the picture which is great but the speakers produce a background noise coordinated with the(mainly male) voice as they are talking. I have heard this noise from female voices also. Seem more prominant at times. I had talked to Panasonic techs and did what was recommended by them. Like by passing all components and providing a direct video source to the tv. At that time I noticed no audio distortion (daytime) over several channels. And reported back to the tech. But come evening with the original hook up again the noise. It's like wwww www wwww ww in the background matching every word that is spoken. Any ideas? Please help if you can. I didn't mean to write abook.