As of yesterday the car started doing this rattling noise that only happens about 1/10 times- ill be driving and rev past 2k rpm and then lift and as the revs go back down theres a rattle noise coming from the engine bay area although while inspecting the car with the hood up i couldn’t replicate the sound. My theory is that its either the belt tensioner which i’m hoping its not or its the heat shield being rattled by something because there is already a previously existing rattle noise from the exhaust being redone and fastened poorly by the shop that the previous owner went to. If anyone has had a similar issue or more experience with how to identify a bad tensioner/heat shield please let me know!

-the noise only happens between 1.5-2k rpm and only when decelerating

That sounds like a classic broken tack weld or loose clamp on a heat shield responding to a specific engine harmonic. The parts drawings show most of the shields on your M are clamped, so pry around with a screwdriver to locate any broken or loose ones.

ill take a look at it when im able to put the car up and get under it. thanks for the help fingers crossed its just the heat shield and nothing to do with timing that sounds like a nightmare.