Buzzing/whining noise from headlight

Hi gang, I finally got around to making an account. I've been having an issue with my Gen 4 (2017 Four) for some time now and I have not been able to find information on it ANYWHERE on the internet. Maybe it has only ever happened to me. But this is what's been going on, and what I've found out about it so far.

A few months after buying my Prius, the wife and I stopped for dinner one night and noticed after we stopped the car that there was a buzzing/whining noise coming from the front. After turning off the engine, we could still hear the noise. It wasn't until we hit the lock button on the key fob twice that the noise stopped (when the headlights turned off). It's possible that it did this the whole time we had it-- we hardly ever drive at night.

The noise only comes from the left headlamp. The right headlamp is completely silent. The daytime running lights do not cause the noise, only the low and high beams. The headlamp makes this noise without fail every time it's turned on. I don't know whether it has gotten louder over time or just more annoying to me, but at its loudest it was clearly audible inside the house while the car was pulling into the driveway. I would say it was about as loud as the noise made by the ICE engine when idling, but higher pitched and more annoying. It sounds distinctly mechanical, and when turning the lights off the sound goes down in pitch before becoming inaudible, as if something were winding down.

Today I had a spare hour and I decided I would futz around with it and see if I could do anything about it. I found that pressing hard on the headlight assembly in different directions could cause the sound to change pitch. I also found that working the headlight aiming screws could cause a change in pitch too. In desperation I tried whacking the lamp assembly with the meat of my palm while it was running (and making the noise), and after a few minutes of this I did get it where it was almost silent. The light was out of adjustment, though, and when I went to adjust it back the sound returned. Once I was happy with the aiming, I pounded on it some more hoping I could get it to shut up again. It didn't seem to work as well this time, but eventually I did hit it just in the right spot to make it almost silent again. It's still louder than the right, but I can really only hear it if I put my ear up to it. I'm sure it will come right back as soon as I hit a good bump.

I'm utterly baffled by this, and by the fact that no one else seems to have ever reported it. I haven't been ablt to find any diagrams of the lamp assembly but maybe there's some kind of cooling fan in there that's gone out of whack? Anybody have any insight on this?