[BuddhaPilot]

I got to drive a new 650i convertible about a month ago and noticed the "bass hit" sound when shifting in sport mode only. Seems like it was only under moderate to hard acceleration. I figured it had to do with the flapper valve or possibly from turbo blow-off dumping into the exhaust tract during the shift. It was definitely distracting. My salesman didn't have much experience with the car as it was the first new 6er they'd received. He was a little startled by it too since he'd never noticed it either. Definitely strange and not something I'd like to hear all the time.