Yep, Uneven pad transfer.
Here's a great source for info on why this occurs and the science behind it.
https://centricparts.com/resources/r...ry=Whitepapers
I've used this and it works to remove the old transfer material so you can rebed the pads:
https://www.amazon.com/Brush-Researc...07INTEMC&psc=1
Sometimes if the brakes have been heavy used/abused while the pulsation occurs, the rotor can go thru a change metallurgically. If that happens then a simple removal of the old transfer layer will not work.