Annoying sounds from cars at stop light

I’ve been inside one of those cars, actually a full size Cadillac SUV that one of my much wealthier than me friends owns. He has a mega dollar audio system at home and spent serious money to upgrade the system in the SUV and I must admit the sound quality - with all the windows rolled up, is really excellent. The bass is clean and layered and very warm and pleasant even at moderately high decibels. No shaking or vibrations whatsoever. Never heard it from the outside though. I guess it all depends on the quality of the car and the system inside. 

" You are correct about very low bass notes having very long waves. Not sure those 6" speakers in the door or even a 12" sub in the trunk are pumping out 30Hz bass loud enough that I can hear it from my car in open air."

Chances are you are not hearing the speakers in the door as much as the subs located somewhere else in the vehicle. Since low bass is non-directional, placement is not crucial. The sub or subs might have dedicated high power amps too. Some systems I have seen have their own battery & capacitor circuit, separate from the vehicles. 

Yes,  I know it’s a good question. I only ask good questions. How do you get low bass with zero volume? You don’t have to have any experience with headphones to see what I mean.

"How do you get low bass with zero volume? 
You don't, you need gain.