Welcome to the M3 cowbell club! I also hear this on the new M3 videos, so don't feel too bad...it's gonna be with the new generation as well, LOL!
Yours doesn't sound too bad. Do a search and you will see a ton of posts.
Does yours appear once in a while? Does it ping at low speeds, driving at slow parking lot speeds?
When I took mine in to the dealer, the sound magically went a way.
I can usually shake off the sound by pulling and releasing the hand brake a few times in a row.