I agree w. Stoney but will add that if the caliper is seizing, the ABS may be sensing this and pumping the system in an attempt to correct it. When this happens at low speeds, it can sound like a quick series of deep twangs. My advice is to get two new/rebuilt calipers and do both the front wheels at once. Also bleed the system, but remember to clamp the lines going from the caliper to the ABS unit so dirty fluid doesn't get into it.