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I have the exact same issue after updated to 2020.12. I was on 2020.4.1 and no issues ever before update.
A reddit post also about this issue: 2020.12 Bluetooth disconnects audio on M3 : teslamotors
~65db is a pretty reasonable noise for Model 3. Though there're many ways to improve it like a door seal.
Anyway I can never reach 50mph on my daily driving at city streets. lol.