E90 M3 Diff sounds like a bag of rocks above ~25-30mph

[flinchy]

How normal is it? I've got black powerflex mounts so pretty close to solid, and solid subframe

There no metallic pinging, no grinding, no whining, just a really loud rumble, like a container full of rocks 😂. Can feel it if I put my hand on the diff. Everything seems to spin smoothly otherwise.

Only just got it installed so haven't gone for a proper drive and got it hot to see if it improves but it's THAT loud.

This is just under normal unloaded acceleration jacked up, not turning or anything with load.

Here's a video of it, after I rev and it sounds like exhaust rumbles, it's not exhaust rumbles