It could be a bad component, or a dead one. Some receivers have heatsinks that cool down certain components, and yours is probably overheating, and the audio processor is dropping out. I have an older Kenwood surround receiver (Late 1990's) in my house, and it does heat up a little, but doesn't drop out the sound. You might want to open it up, and have a look inside for any obstruction of the cooling mechanisms, like dust, and corrosion.