Samsung BD-P3600 problems with sound

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I have a Samsung BD-P3600 Blu-ray player and have had a recurring and annoying problem. It started a few weeks after first use. A DVD that I had been playing OK lost all sound. Ejecting it and reloading did not help. I put a blu-ray disk is that I played earlier without a problem had no sound either. If I went into the player's setup (no changes) and then playing produced sound. I turned the machine off and turned it on a few days later to demo the unit for a friend. Sound was now back. A similar problem happened a week later. Now yesterday, after playing several DVDs with no problem. I inserted a blu-ray disk. Result was no sound for the blu-ray disk and also for the DVD that I had just watched. Anybody run into this or have any ideas?

P.S. The player is completely up to date on software