It's probably the cable box authenticating the HDCP (copy protection) measure for a different channel.
I'm not sure there's a way around it, and there's not a way to disable the channel box at the top.
--HDTech
I've been searching around for an answer to this with no avail. Just purchased last week a LN32A450 for the bedroom. When I change channels on cable channels, when the little box that displays the channel information goes away, the sound cuts out for about a half second. Does not do this on over the air HD/digital channels, only on the cable channels. I have the cable connected directly to antenna in and using the built in speakers in surround sound mode. Anyone know a way around that? Thanks.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic