White Noise?

I've been quite bothered by the sirens and random distracting noises that exist within the city. Aside from the common ambulances and VIP Cadillac that zoom through loudly, there are several very obnoxious grates on the streets like the one on the corner of Virginia Avenue and E Street NW by the CVS. Do you know why they make such a deafening sound? It's like there's a supersonic jet preparing for take off underneath! My latest strategy is to avoid such routes.