I also recognized this behavior for a while that it takes a long time until the box responds again after choosing audio settings. I don't know where it come from but I didn't have these problem any more.
Compare your audio settings to mine from this post:
Maybe the red speaker icon on the screen is the mute sign. I had in the past sometimes also the problem that I pressed a button and suddenly mute was activated although this button wasn't configured to it. So I had to use "keymap editor" addon to assign the mute function to any button from my remote to deactivate it. Then I deleted these assignment again to have the original function.
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