NVH = Noise, vibration, and harshness
When you turn your steering wheel, the struts turn, and the springs turn with the struts. The upper spring perches have bearings above them, which allow the springs to rotate smoothly.
I suspect that the noise is coming from one of these mechanisms.
Best way to find out for sure? Install the factory upper mounts.
E92 M3 DCT - AiM EVO4 Data Logger / AiM SmartyCam HD / KW Competition 2-Way / OMP ARS Racing Seats / Brembo GT 365 / Pagid Yellow RS-29 / Rear Seats Delete