Yeh thats exactly what mine was doing Riko, like a nasty grinding sound and the abs light was coming on and off, like you could feel it kicking in and out, but at very low speeds. Must be a speed sensor. Is worth changing them both or just the faulty one? I guess if its just picking up a fault on the left hand side one then the right hand side one must be fine, if it aint broke dont fix it!