I think you may be under-appreciating just how loud an internal combustion engine is without mufflers. I suspect that the big issue with LLVs isn't that they are particularly loud (they are louder than a typical modern consumer-oriented car fresh from the factory, for sure, but pretty similar to other purpose-built delivery vehicles), but that they have a very distinctive tone. You hear it once a day, every day, so it becomes something your mind picks up on as a pattern.