Running around, stop and go in a city, the maximum load normally wouldn't be all that high. The REx engine will adjust the RPM to help match the load. It's quite possible that it would run fairly slowly under those circumstances. Take it out on the highway, blast up a long grade, and your results will likely differ. But, there'd be more wind and tire noise, so you still may not hear it.
2011 535i x-drive GT, 2014 i3 BEV
Soon (hopefully!) A 2021 X5 45e will replace the above