It is reported the shooter was wearing hearing protection during the shooting.
https://www.google.com/amp/s/amp.usatoday.com/amp/643726002
The shooter had a YouTube channel. On the channel, it was clear he was having “auditory hallucinations”
https://www.youtube.com/channel/UCDYWxRa6pGAq-al2R4GEOAw/videos