Loud Whine/Whistle, 37" Magnavox lcd

I have a 37" Magnavox lcd widescreen hdtv, model 37MF321D/37. My problem is that the tv makes a loud whine/whistle noise that comes from a distinct area on the back of the tv. The whine becomes louder when the screen produces a brighter(higher contrast) picture and softer when it gets darker(changing channel, dark scenes).I know it's not entirely the speakers because the noise is still present after disconnecting them. However, although the speakers do not produce the sound, it does amplify the noise much louder than what the tv normally produces(when i mute the speakers the sound is still present, but not as loud).I currently have my tv cable, xbox 360 and pc hooked up to the tv. The whine is unbearable when watching tv or playing on the xbox, but is not noticeable when on the computer. Since the computer has its own speakers, the noise is not amplified through them.

The tv has been like this for almost a year now and I'm starting to go crazy. I would like to know what the problem is, is it easily fixable,and generally how much it would cost me to get it fixed. It cost me around $800 about 3 years ago, so is it worth it to get a new TV or try to fix it?