my tv has a buzzing sound, even when on mute. tried changing audio selection...

Sounds like it is the connector for audio. If you have it running through stereo or typical red yellow white cables then there maybe some interference coming from the cable connections. Test by trying different channels and removing connectors then turn volume up if buzz persists after connectors removed it is tv. If buzz changes when you mess with connectors then it is in the connectors. most cheap connectors are not shield properly and they let electronic interference in which causes buzz. May also be the connection inside back of tv that may have become looser and now causing interference. If ONLY MTV then may also be cable company having bad feed problems. So try new connectors, after you have removed current connectors and turned up volume.