Mysterious brake squeak (mechanic is stumped)

I'm hearing some mysterious squeaking/squealing on the rear brakes of my 2014 Prius V. It sounds like a barking sea lion. It isn't present all the time and it seems to be worse when it's cold/wet out. It's especially noticeable when I first start driving in the morning. Lately, the sound has been getting worse and I'm noticing it at highway speeds, which wasn't happening before. Sometimes, when I tap the brakes, it goes away for a little bit, but then it comes back.

This started a couple years ago when I had the pads and rotors replaced by my old mechanic (now retired). I brought the car back in and he said he couldn't find anything wrong and not to worry about it. I took his word for it and kept driving.

Fast forward to last month (January 2026) when I had to replace the pads and rotors again to pass inspection. This time I decided to do it myself to save money. The guy at NAPA recommended SilentGUARD, so that's what I put on there. I haven't done my own brakes before, so I followed the directions in this video exactly:

The car passed inspection, but the squeaking remains.

Since the squeaking is getting worse, I decided to check in with the pros. My new mechanic took a look this morning. I just got off the phone and they said they noticed a weird "cross-hatching" pattern on the rotors and think that's the problem. Aside from that, though, everything looks A-OK. As far as they could see, there was nothing wrong. It was the shop foreman who did the work and he said the calipers were operating "like buttah."

They want to replace the pads/rotors again, this time with OEM parts ($820). I them that I was concerned that the unusual pattern was a symptom and not a cause. I'm mostly worried that the problem will just come right back again. The mechanic said he understood and also that he was stumped. In 30+ years of fixing cars, he'd never seen anything like this.

I'm not sure what to do! Can anyone offer advice on how to proceed?

 

I did some more research. This sounds exactly like what I'm hearing:

The person who posted this video says the problem was fixed by Toyota T-SB-0081-13.

I'm still not sure what to do. Should I bring this information to my mechanic? Or should I take the car to a dealership? (Would I be correct in assuming that the dealership would most likely charge significantly more money?)