Another ex BMW driver and I can't say its any quieter in fact in some regards its noisier. My last BMW had an annoying rattle that turned out to be by watch strap to give you an idea of the noise level. The Model S has a whistling noise from the wing mirror and tyre noise.
I think the bigger change is maybe oddly less about Petrol to Electric, it the culture or ethos of the car. The software updates are a mixed blessing at times, some stuff isn't finished or works poorly compared to what you might expect, and there's lots you might expect simply missing (carplay, 360 parking cameras, adaptive headlights, different suspension settings, foot opening of the boot, soft close doors etc), but then there's other stuff to win you over. If you expect a car thats everything you had before plus extra high tech with a minimalist design, you might be disappointed, if you just want something different, you'll enjoy it. I'm amazed how many people have paid £2k to upgrade their MCU (big screen) on the older cars so they can get netflix and a few more games plus traffic cone visuals when you could buy a £500 ipad that does so much more but thats the way it seems to be.