Popping Noise From Back When Braking

When braking I hear a loud popping noise that appears to be coming from the rear driver side. The sound will continue until I release the brake pedal. The rear pads were replaced about five months ago. Any thoughts on what it might be?

Were the rotors replaced or turned? Sliders lubed?

They were not. When I put on the back pads I did use some braking quiet compound on the back of the pads where the piston makes contact.

Rotor cracked?

Wonder if the piston is sticking in the caliper, and then it suddenly releases, and slams into the rotor?