I'm super sensitive to noises as well, especially "out of the usual" noises. It's about catching a small problem before it becomes a big one.
It sounds like you bought the car used with a few miles so you don't know what's normal for your car. If it's always been that way since you bought it and drives ok, as other stated, it's probably ok. But also, as others have stated, keep getting different opinions.
A really good tech might be familiar or be more willing to spend some real time in diagnosing your issue instead of the "it's an M3"-thing.