I hear it when Im just coasting along at lower speeds (about 15-30 mph). Its kind of like a "knack knack knack" sound... seems to be correlated with the tire spinning as far as how fast the "knack" sound repeats. It completely goes away when I depress the brake pedal. Let go, comes right back. It sounds like it may be coming from the front, but Im not really sure. Any ideas?