Annoying sounds from cars at stop light

I would say that the wall may ’seem’ to amplify certain frequencies. The RESONANT frequency (or a multiple of it) of the surface..So it can seem to be amplifying a particular note... Taking the wider band of energy and focusing it more on the resonant frequency. Same is true of speakers..

I would agree Elizabeth. Pretty accurate read on the issue. Sound waves are altered, Some frequencies don't fare well in sheet rock and lose amplitude. Others, like the dreaded 80Hz bass notes, ( those lease busters ) get amplified. 

Alternative explanation: the poor guy upstairs or in the next apartment only hears the bass frequencies but not the rest of the frequencies. That’s why the sound is irritating, it’s just the thump, thump of the bass, not because the bass is amplified. The wall absorbs higher frequencies better than low frequencies.  If it was true walls amplified bass frequencies you could get better bass by constructing a wall in front of your speakers. Hel- loo!

My sound system makes a glorious sound at lights. It's called a Hemi.

I had one of those cars and when I went to the gas station all I heard was a guzzling sound.........