My HD rear projection RCA TV has a very high pitch reverberating whining noise coming from within the TV case. My audio is all through my Yamaha Surround Sound. The sound is clearly coming from within the TV case.
If it is a DLP set, the sound is your color wheel going bad. The sound usually is accompanied by a picture degradation (crummy fleshtones). I am not aware of the wheel being sold separate from the light engine. You may need to price a rebuilt engine.
If it is a true crt-based rear projection, that is your flyback transformer taking a poop. That module is on your power deflection board, which can only be rebuilt, not replaced.