Slight audio problem with the xbox 360 or tv..?

so i recently got an hdmi cable for my xbox, since i purchased a new flatscreen tv not too long ago. A few days ago, I noticed that every 30-40 seconds the sound decreases to almost mute, but only for a split second. Playing games or watching a movie, it does the same thing. Does anyone have any idea as to why this is happening? Its a small problem, but it gets rather annoying. thanks.