What kind of noise are you used to on the expressway in an ICE-powered car? If you've driven a MINI Cooper S on the expressway, you'll definitely be in a quieter environment in an SE. However, the road- and wind-noise are still there. I don't believe there is a ton of sound-deadening insulation in any MINI Cooper, so it's noisier than driving a luxo ICE-powered car--or even a Honda Accord.
Some long-time MINI fanatics rue the SE's loss of the exhaust note. I see it as a big advantage--but more for in-town driving than on the e-way. I love how I can accelerate so quickly without the attendant audio-drama a red-lined engine broadcasts. Short bursts of speed don't cause people (especially people wearing badges) to turn their heads and take notice. People interpret the sound of an engine winding out as an attempt by a rude driver to show off how loud and powerful his car is.