At least at the Washington border, there are large signs telling you to turn off your engine while in line. Presumably this is for environmental reasons, but there maybe additional benefits.

From what I understand about speakers, a vibrating piece of glass would be an amazing one. Especially for sophisticated equipment.

I bet you could remove it fairly easily. Use another laser to count the revs or something. Your brain does most of the work in removing noise from speech.

I don't think it's that straightforward, a few feet of difference in source position amounts to a phase shift of significant percentage of a wavelength at audio frequencies. You can't just flip phase and sum. It was also my understanding that laser microphones require very precise alignment, and getting one lined up normal to a convex, moving windshield is at least a tiny bit more than "trivial"

Or just use two microphones—one aimed at the windshield and one at the bonnet—and subtract one from the other.

Then it turns into a significantly more complex problem. The thing with removing noise from speech is that the amount of vibration from the glass due to speech is negligible compared to the vibration due to the motor