I was also having this issue but after removing the contents of the sounds folder and verifying the files it seemed to fix it, but I can see you have clearly tried that to no avail. Forwarding to the audio team to take a look at.
Edit: So, apparently there is some sort of corruption taking place during the download that we are currently working on a solution for. For now, we can only suggest that you try to verify the files again. Please accept our apologies for this.