I have encountered another sound bug (PS4 Pro, latest version of the game. Playing in stereo (my PS4 is set to output 2ch 48KHz PCM through optical output)).
It happened only once, I think I got hit a few times (you know the sound gets muffled when that happens ?). Well, the sound stayed muffled for the whole race after that, it was almost mute.
I couldn't reproduce it at will but will let you know if it happens again. This happened in an online race (can't remember game mode, it was the 2048 campaign ).