[Jdawgmasta]

Hi all,

Discovered a new noise over the past few days. It's a low hum from the right rear that I can only hear from inside the car. Sounds like an AC vent on medium.

From a cold start, the noise gradually goes away over 5 minutes. If I turn off the engine and restart, the noise comes back for 10 seconds then abruptly cuts out.

Has anyone have something similar come up and can point me in the right direction? I figure it's exhaust related but I can't explain why the noise comes back when I start preheated. Thanks.
(I'm reposting this from BmwTech subreddit)