That sucks. One reason I love my neighborhood so much. No HOA, no picky neighbors. I want a nicer/larger home but that would mean pickier/snobbier neighbors. They are probably the types who take the car to the shop for everything and believe that the garage door should only be open when driving a vehicle thru it.
My brother had a similar problem with his 4 vehicles that were always undergoing some sort of "refit" It wasnt the police, it was code enforcement. All the vehicles were registered and the grass was always cut. After the 3rd visit from code enforcement snooping for something they could pin on him, he shared his new "landscaping plan" with a few of his neighbors. It included....
Tons of wooden cutout statues in the new "curb to porch" english garden.
Pink Flamingos, lots of em.
Picture window graced with an American flag
And his minivan painted with a new "military camo"paint scheme.
Funny how the complaints suddenly stopped
You might consider dropping some similiar hints
Edited to add: The pipebomb thing isnt funny at all, please do not even give that a moments consideration.