I vote for something along those lines.
Or, the elevator is a spy drop, and the quarters are embedded with top secret info and the OP is totally screwing up our national security. 
This.
A petty ante robber, fleeing the gendarmes, hid in the elevator shaft and was killed.
Everytime the car passes his body, some of the loot falls into the car and rolls to the grate.
Because duh, free money!
Well yes, but I’ve heard that folks urinate in elevators and there must be nasty stuff tromped in that finds it’s way to the grates.
Where did you hear that folks urinate in elevators? I don’t think I’ve ever seen that, and I take a lot of elevators.
And in my apartment building, things are cleaned every day.
Boo Radley is doing it.
At least at one light rail station in my area, the elevators used to get people from the train to the bus (or vice versa) always smell like they’ve been used for a restroom (in that part of town, they probably were).
Then there’s this gem from Passive-Aggressive Notes.
Guys coming home from parties late at night.
Winos who wander into the building.
Folks annoyed with the landlord.
Googling finds thisand other links.
Wash those quarters!
“Hi, Eyebrows, it’s me, Mitt. Do you know who makes these money-generating elevators, and if they do them in car sizes?”
That’s really not that common, though. In my building it’s pretty much unheard of.
This reminds me very much of the children’s book “Willie the Squowse”.
I’m glad.
I’m loving all these responses! Let’s see if it happens again tonight!
Oh, and my building and elevator are very clean, so I have no worries about people urinating (lol) in the elevator. It’s no different than just picking them off the floor.
Maybe a bag of change broke showering quarters everywhere and a few get worked loose every day.
I just hope these aren’t some kind of offering to a dark force and that you’re not going to unleash that force by taking away the only thing that appeases it - spare change.
Good gad, Cheap Evile Demons are the very worst!
It’s a giant vending machine; sometime soon, enough money will have been inserted, and the floor will open.
I’m guessing a child is doing it.
It’s the new form of economic stimulus
That was my thought. I recently found a magnetic number (the kind kids like to play with on refrigerators) stuffed into a crevice on my dishwasher’s door (I assume this was from a prior tenant, since I don’t have kids).