Yeah I live in an area where farms and ranchettes are just getting converted into neighborhoods and there is a "custom diesel shop" behind the neighborhood.
They clearly are not good enough mechanics to make a living at doing it, and they have their own virtual junkyard out there leaching who-knows-what into the soil.
The worst part is they tend to do their testing and tuning at the odd hours of the night, since they clearly have day jobs. They tend to roll lots of coal when they are testing and it ends up in people's backyards. So not only is it loud at 1AM, but they leave soot all over the place. I actually don't usually get the soot in my yard but I can hear them revving up the diesel motors they work on and it is loud.
The houses that are worst affected by the soot, the original owners actually sold their houses and moved away. Sad.
The HOA has tried contacting almost every governmental organization out there to stop them but to no avail. Their excuse: We were here first!
This is the outfit: