help identifying this loud screeching/scraping noise (sound file attached)

I started hearing some weird sounds including repetitive scraping this morning on my way to work. Sure enough, it was coming from my Prius but then went away. After work, I was able to repro it again but eventually it went away, it seems. Zip of recording attached. Sorry about the file format. It's what my iPhone emits.

Any guesses? Scraping brakes? I fairly sure it's repro even when not braking and it's repro if I shift to neutral while coasting and even if I shut the power off (press + hold power for 3 seconds) then coast. This is all at low speeds (<15 mph). I don't know if it's audible at higher speeds. I've never heard anything like this from my Prius or any car I've owned before.

Try to ignore the wind noise and ignore the banging in the middle of the 2nd recording. It's from running over a metal strip inside my work's parking garage. Although the sounds might seem faint in the recording, they're quite loud w/the windows open.

I slammed on the brakes and I think it went away but I swear I heard it faintly again once on the way home. I'm at just under 46K miles now.

The closest Toyota dealer to me (and one I trust) is 6.2 miles away... I'm not sure if I should get it hauled on a flatbed truck (it'd be likely be out of my own pocket) or risk driving it to the dealer. Luckily, I have another car...

 

Yeah, I hope I wouldn't have worn out any brakes so quickly as I'm light on the brakes to aid in regen. However, I did multiple tries of the full throttle + brake test recently (was trying all 3 stopping methods in Luscious Garage's video).

 

The dealer felt my parking brake was out of adjustment (didn't hold the car well) so they figured they'd do that as part of taking things apart to diagnose. They said they checked the front brakes too and couldn't find anything wrong and the fronts and rears weren't worn out. They also couldn't repro the noise. :/

The service advisor suggested the same thing as you did.

When I arrived, he asked if I drive on gravel roads. My answer, no. After I left, I realized that's there been this damn road construction near my apartment on the way to work I have to go through every day. They're digging and doing who knows what? Maybe I picked up rocks from there...

They only charged me for 30 mins of labor so it was ~$53...

 

Forgot to mention w/all the damned road construction, there are piles of gravel on the side of the road.

Side note: A woman w/a 2010 Prius was behind me in line for an oil change. She thought she needed it b/c her light came on (maint reqd?) but the service advisor I think was explaining to her that the interval got changed to 10K miles. She was unaware and seemed skeptical about the increased interval... something about what her husband thinks... blah blah. I wasn't trying to eavesdrop. I think the advisor finally talked her out of the oil change and was going to reset the light for her.

When she first arrived, I asked her if she was going to have the brake reprogramming recall work done and she said nope and seemed resistant to it. She said she was just there for an oil change and felt the car worked fine and didn't "want to have to change her engine".

I later spoke to her about what the recall was all about, mentioned the 20 minute job, video online, etc. and the braking brief dropout sensation. She knew exactly what I was talking about but she didn't think it was big deal. I informed her about the recall being to correct that.

Just goes to show an example of the range of Prius knowledge out there...