We have a 98 GMC Burb, 138K, 4WD. While driving slow on level ground, there was a sharp snap or crack in the left front. Sounded like something broke. Drove the 1 mile to home cautiously. Pulled in garage and there is brake odor. Pulled left front apart, expecting to find bad caliper etc. Found nothing. Put back together. It drives straight, smooth but can still hear something making occasional noise. Only thing different seemed to be the brakes grabbed after a few seconds on the snow rather than pulsating. Need some help in how to determine the problem?