It's stretching, and when you take your foot off the brake, it pulls the piston right back where it started from. The most likely time for this to happen is right when you change your pads, because you've pushed the pistons back in the bore, where the walls may no longer have a proper finish for smooth sliding. Brake Rotor runout can be caused by several things: variations in manufacturing tolerances, sloppy resurfacing procedures, a 2. What else can cause brake pulsation problems besides the rotors?
Check the flasher switch while you are behind the dash. If you still can't create the intermittent problem, I suspect you need to chase the ground. My problem ground was the tail light bucket contact. A gound wire from the harness connects to the tail light bucket. Easy to take apart & spray both tail light buckets with the contact cleaner.