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.