So I'm getting this noise (and vibration) from the rear like my hub is busted, or the wheel is about to come off.
Having checked that the wheels are secure, I've checked the hubs (they're fine), half shafts were replaced recently, brakes were just swapped, so, what gives?

Is my diff going south?

 

We could use some specifics to help determine the exact reason for the noise.

Off the top of my head, it sounds like tires or something got goofed in the brake swap.

Check your driveshaft too.

 

Noise was present prior to brake swap