Received a call back from a Tesla Mobile Service Agent but I didn't catch the call in time so it went to voicemail. Going to call him back shortly. Here's the transcript of the call. Luckily it sounds like they are aware of the issue and working on a fix:
Hi this is Devon from Tesla mobile. I'm just calling about the issue you're having with the diminished sound quality especially with the subwoofer. So we had a couple technicians look into the situation, they are currently still working on part of the fix for it but there was one issue that had been noted from the older firmware that was causing this, but the newer version should be clearing it up. We did load it onto your vehicle a couple days ago, so I was calling to see if that resolved it and if not then we can schedule an appointment to have somebody come out to give a listen to it and see where we go from there. I do have a couple spots open tomorrow so please give me a call and I can get you booked in. My number is xxx-xxx-xxxx, thank you.
Hopefully we have some forward progress now.