Found this on the net.Maybe give it a try?
The gist:
If you select "Use Side Switch to:" lock rotation when previously it was set to Mute, and your side switch was in the mute position when you switch the toggle from mute to rotation, it thinks that it's still on mute.
Anyways, the solution is just to flip the switch to the unmute position, go into settings and select "Use side switch to: MUTE" (then switch it back to lock rotation if you'd like, BUT don't play w/ the side toggle while doing so).