I have a 2005 chevy silverado 4wd crew cab. When coming to a complete stop the pedal suddenly goes down a little farther and I hear a noise like a groan (ABS pump?). I had a brake line leak awhile back and had to replace a line at the rear of the truck. I bled all the brakes and replaced the master cylinder. I bled the ABS system using the Autel MaxiCheck scanner and it still does the same thing. Any ideas?