Brake Whistle-like Noise

2008 Tundra, 5.7, Crewmax

At slow speeds I get a whistle when I press the brake petal. I also get a whistle when I let off the brake petal. The noise seems to be coming from the front half of the truck, and best I can tell from the driver's seat is the noise is coming from under the truck.

I suspect the noise is a vacuum leak of sorts and associated with the brake booster. I have not confirmed this.

I've searched the best I can and cannot find a similar problem that also includes a final result. Any help is appreciated.

 

Gonna have to get under the hood and check the brake booster vacuum line and booster. Brakes acting normally? Definitely a whistle and not a screech from low brake pad indicator?

 

Brakes do work really well. Here’s a video. Now I’m thinking it’s coming from the rear axle area. I’ll try and get a neighbor to help me pinpoint.
https://youtube.com/shorts/z30G0uqtas8?si=bkddnugXrfDS86yi