NEW high pitch whine (louder outside car)

Hi there. Brand-new sound yesterday driving on the highway. It was sporadic and mostly not happening, but it was a very high-frequency whine, non-changing pitch. Didn't really sound like inverter/"CRT" high whine, it was a bit more substantial, meaning maybe lower frequency that that almost supersonic sound. It sounded like it was coming from the rear of the car.

I opened the windows and it was louder, so it didn't seem like it was originating in the interior of the car. I couldn't quite map it to any particular "states" (meaning IC engine or coasting or EV modes) because I was going about 65 up and down hills and it seemed to just start and stop at random.

One thing I will note is I got my oil changed and you can see the schmucks who did it didn't button up the plastic shield/door properly underneath. It's like 2-3" off the ground and messy, so I wondered if it was wind going through it, but it really sounded electronic or like a mechanical squeal. Any ideas?

 

Afraid I don't have any besides that I was doing highway speeds and going more or less straight. Didn't sounds or feel like a wheel bearing and I didn't hear it at all tooling around at low or highway speeds today. However when I started the car today it kinda did an initial rumble which made me shudder a bit. I hope it's not related, but perhaps I turned it off before it went into EV mode (I've had this happen occasionally when turning it off during a warm-up cycle). OR my HG is going...

I don't like to comment on physical appearances...but after my sanctimonious comment there, I'll be a total hypocrite and say this dude looked like he was out of central casting for an ingrate. He got out, grinned and said "I couldn't reset the maintenance light!" and threw me the keys. Haha! Maybe that was a tell. I pulled over in the lot, checked the oil level and reset the light. Stupid me forgot to look under the car, though.

 

It hasn't done it since but if I can get it regularly again I will.
I'm now getting rough starts...the worrying noises tend to come in clumps.
Cylinder misfires. Maybe I'll no longer be a Prius owner soon.

 

None yet - get the occasional P0A80 because battery is original. I reset it with my phone and keep going.

The rough start definitely is freaking me out. Coinciding with the loose plastic splash guard, I first hoped it was that vibrating, but it doesn't seem to be the case. Plus that would keep vibrating. This just does it for 10 seconds max on startup then smoothes out for the rest of the trip, which seems like a HG thing.

 

Engine light on start today (ironically, it barely shuddered this time).
F##k.

Will passing (reasonable percentage) a leakdown test point to an EGR problem?