Anywho..regarding the OP... I really, really related to the latter half of it..i.e. thought process re. the doorbell, then them randomly being in the backyard, you initially being somewhat offended/alarmed/bothered by them being back there without telling you, then that feeling backing off once you realized what they were doing and how concerned they were about all of it.
To the first bit about the police (although I read your later post that that wasn't an important element to the story), I would not have done that - especially if I didn't know the neighbors' personalities well enough, I wouldn't want to piss them off for fear that they'd start being subtly obnoxious in the future just to get back at me. haha. I'd probably have walked over and talked to them. BUT I guess the negative of doing that is you could end up with someone who wouldn't much care, and would take forever to fix it, when it would have been better to put the fear in them. I guess there are total unknowns no matter what the choice.
Also related to fidelia's post, re. one minor thing isn't a big deal, and I tend to be pretty mellow/chill about isolated things, but once patterns start forming, the sum of all of the no-big-deals can become a Big Deal.