95 S10 Brakes

Just replaced the front brake rotors,pads and he caliper bolts. I every so often have a thumping sound. Sounds as though I have a wobbly tire, but not so. I tap the brake pedal and the feeeling is gone. this does not happen every time I drive it.Could something be loose or is it possible anti lock problem? front end work? I did have to chisle off rounded lug nut. Not sure what to look for
MURF