Have you tried changing out the cables themselves? It is possible that there may be some damage on the cables or that the cables have degraded and is causing the buzzing you are hearing (which, from your description, actually sounds like interference).
When I turn the TV on I hear a crackling noise. The noise is only present when the TV is on Component source(for cable). When on AV source, no noise. When I mute the TV the noise stops. When I take both Red and White AV cords out of the TV the noise stops. When I put them back in and take the same cords out of the cable box the noise continues. If I turn the cable box off the noise continues. When I raise the volume the volume of the noise increases. I've had the TV for about 3 years. Any thoughts?