Actually, I am the OP. Topic drift need not be counterfactual.
My aim was simply to achieve in daylight what I am often able to achieve with flashing high beams in a parking garage: to get pedestrians going the same way to realize that there is a car behind them without using the get-out-of-my-way horn. Half of those people are my neighbors.
Outdoors, the headlight flash does not work. What I suggested was attaching a noisemaker (programmable doorbell) to run off the high beam feed wire, so you get both a brief noise and a brief flash.
As for choice of noise, I want to avoid startling the people. Or drawing excess attention to myself with a novel noise, in the manner of many flippant suggestions. Life is not a road-runner cartoon.
Engine sounds, however, can be hard to locate as being behind you; they could be from a parked car. Tire noise does imply a moving vehicle but it is often too subtle, which is why I thought of studded snow tires. That would probably work in Seattle, but the suggestion of "tires crunching gravel" would work even in the tropics. The high-frequency components of gravel-crunch attenuate with distance, so when you hear the full range of sound from a nearby source, you naturally think "moving car nearby."
What I want the people to do is simply make room and hang onto kids that might dart. I would prefer that they not think me (and other Tesla owners) rude.
Any other suggestions for how to implement? We need a recipe.