My top list is 1) dogs, 2) babies, 3) lawnmowers/leafblowers/etc. This is why I hate living in areas with a lot of single-family homes. I find that kind of screeching noise pollution much more grating than loud music, trains or heavy machinery - stuff that tends to occupy a lower frequency range.

That said, it absolutely seems reasonable to have a decibel limit on vehicles, in particular to catch the antisocial people who deliberately tune their cars or motorcycles to be as obnoxiously loud as possible. Although, I was under the impression that in most places it was already illegal to register private vehicles that exceeded a maximum noise threshold, and that it would be tested during the annual vehicle inspection. Apparently not?