Great post, it all makes sense and meshes with my own (admittedly limit) experience.
An interesting fact there are two things that get bees defensive - color and sounds.
Lawnmowers and other droning machinery sounds enough like a swarm that the bees can register it as an attack and swarm the offending machine and operator in defense of the hive.
Interesting comment about the color and sounds triggers, I had never heard about that. Yet it squares with an experience I recall from a couple summers ago...
I was mowing the lawn in front of my house. Using an electric (battery-powered) lawn mower (great machine, by the way..). Unlike a gas-powered mower, it definitely "humms" (and is moderately loud - much louder than a drone but a lower pitch).
Happily mowing away, I suddenly felt an intense, sharp pain on the back of my neck. OUCH!! WTF was that? I let go of the mower (auto shutoff) and felt around on my neck. Felt a now-tender raised spot. Checking myself in a mirror, I see a big red welt there -- yup, something bit me! I shrug it off, go back outside to finish cutting the grass and soon I notice a yellow-jacket or two buzzing around me. This seemed odd because 1) I don't recall the last time any bees bothered me (like, it's been decades), 2) they kept harassing me even though I moved away, gave them plenty of space, and waved them off, they continued to come after me, and 3) this was completely out of the blue (I mow the lawn regularly in the summer, have never had any trouble with insects harassing me before).
I abandoned my lawn mowing for the day, and went looking to see if I could find any more yellow jackets. I walked around behind the house and noticed a LOT of them (dozens, by my first estimate). And they were all buzzing around...the roof of my backyard plastic storage shed...which is where we keep the lawn mower. After suiting up in long pants and a hoodie (I had been in shorts and a T-shirt) I took a closer look. Yellow jackets were coming and going constantly in large numbers from the roof of the lawn mower shed. Uh-oh...
Note: I have learned that yellow jackets are
wasps, not bees (they're nasty little buggers, too). Still, it appears they behave like bees in many ways...
I called Jerry The Bee Guy (a local who collects and relocates bees, preferably honey bees, at no charge but he will also dispose of nastier critters for a fee if needed). He came out that afternoon and (dressed in appropriate protective gear) located and destroyed a large yellow jacket nest (about the size of a flattened football) which had been built on the exterior roof of our shed. Problem solved.
Apparently, me opening up the shed doors and rolling out the lawn mover jiggles the shed enough that it disturbed the yellow jackets on the roof, which sent them out looking for a threat to neutralize. They seem to have found me on the other side of the house a few minutes later, and the loud HUMMM from the battery powered lawn mower seems to have identified me as a threat worth attacking.
At the time, the whole experience seemed really weird and completely out of the blue (I was a long way from the nest on the shed, on the other side of a large house) but some of the little buggers definitely went after me. The sound of the mower as a trigger aligns perfectly with what you said
@Brojon, and now the "attack" makes sense. I never connected the sound with the incident. Amazing.