Brake Creak

I have a 2018 Cadillac CT6, and the brakes creak (not squealing) at low speeds. If I press the brakes when parked, they creak as I push the pedal and also while releasing the pedal. Sometimes there is a bit of a "click" sound with the creak.

Have had it serviced 3 different times at 3 different places. First time they replaced the pads and rotors. Creak came back after a week. 2nd time they said brakes were fine and put "copper paste" on them to see if it'd help. It didn't. 3rd time they disassembled the brakes and cleaned and lubed the pistons. Creak went away for a week and is back again.

WTF?

Thanks in advance.