I upgraded the firmware but did not try the "beta" update mentioned in the "sticky" comment at the top of this forum.

After my firmware, update the "no sound" problem was less frequent. When it happens, it almost always happens when my DVD is already playing a music CD when the 970 comes on. Although it has creeped up when doing something as simple as changing channels.
I am waiting for the next firmware update to come out of beta before trying it.