Yamaha DVX-S120 System "receiver looses sound changing" Questions

...receiver. On occasion, about 5 minutes after switching the unit on, a high audible level Air sound comes out of the amp -- only switching off the unit and powering on again removes the interference. ...

...sound is shutting off when theres a loud noise in the movie. I changed the cables and its still doing it . i have it set up through digital optical. is the tv causing the problem or the receiver? ...