Why do some people think that driving around while playing loud music makes them cool?

I don't know, either. Maybe if it's loud enough, they don't have to think.

I think they just want people to try and find the source of the noise, that way people might notice them.

Could be. I've been wondering about people in thin NW corner of New Mexico. We have a coffee vendor called Durango Joe's. Fine. So people like to drive up and get a cup of their coffee. But why on earth do the need a bumper sticker that says "Powered by Durango Joe's"?

Makes them stand out from the great unwashed crowds?