Cable or satellite signal? Do you have another TV to see if the sound cuts out there, too?

If you can isolate it to this TV (not the cable box, incoming signal from the cable co, etc.), then it sounds like a component heating up over time to the point where the circuit stops working. If the picture is not affected when it happens, it's either in the audio portion of the tuning circuit, or in the audio amplifier circuit. It will probably get worse over time as that component wears out and eventually fails completely. Unless you are one of those rare people who is willing and able to pick up a soldering iron, you'll have to take it to a repair shop.

Randy: I do have another TV that does not have the problem.

Crusadr: I believer you hit the nail on the head. I can't repair the TV myself. Wonder how much it will cost to get it repaired.

Thanks for your replies and guidance.