I replaced my brake rotors and pads on a 2006 Ford Ranger XL 2.3L 2WD yesterday. I replaced the front passenger side brake, then test drove the truck without any issues. While replacing the driver side brake, I noticed inside of one of the caliper pistons beads of liquid, I'm assuming break fluid. There are two pistons, and one had almost no liquid, while the 2nd had a noticeable amount of beads of liquid. Now when I brake, if I'm going very slowly and at when the brake is almost completely depressed, I hear a low humming sound, and the brake pedal seems to momentarily drop back just slightly. This also happens when I'm going down hill and breaking. For the most part, the car brakes completely normally, and it's only every 4th or 5th time braking that this happens. Again, there is a low humming noise when it happens. Does this sound like a fluid leak in the caliper piston?