Exhaust Valve Opening

I've done some searching about the "butterfly" style exhaust valve on 2 of the 4 tailpipes on the X5M, and mostly seen some questions/answers on other model forums. Nobody seems to know for sure what causes these valves open up. Sorry for my ignorance- I mostly am just curious. At standstill (in all drive modes) they seem closed, so barring a test where I place a camera staring straight into the exhaust and drive off, does anybody actually know exactly what sets these valves off? I assume either heavy throttle load out of necessity or a certain RPM point? Sounds like some people with other models have been able to disconnect it and permanantly open it up for noise reasons?

The valve is open in the M power mode all the time after warm-up. In non-M it seems to be regulated by manifold pressure/vacuum. My M3 was a pneumatic/vacuum valve but I haven't crawled under the X5M to see if the valve is electric or vacuum.

Are you the same Wine Country who posts on the UA forum in FT?

Thanks for the info! And no, I don't think thats me