Sounds a familiar tale. I have the same issue on my 320i. Sounds a bit 'throaty' whilst running - not especially noticable whilst driving but dreadful from the outside! I have the same questions you have posed.

Mild chip fitted. Followed the chip replacement guide and it was a very easy process. The car is definitely better with the new chip; noticeably more responsive on the throttle and acceleration.
Very good service from Speedtouch with regard to questions / guidance .
One happy customer.
Cheers.