Suspension knock

three weeks ago I replaced the struts, ball joints, tie rods, put in some ford racing lowering springs, new sway bar, end links and bushings. After which I got it aligned and new pony mags with some Kelly springfield tires. Not consistently, but every 4th or 5th time I take it for a drive, when I go over rivets in the ground or bumps, I get a knocking and a loud crack underneath my car. I've taken it to my shop and looked, also took it to two shops apart from my own. Anyone experienced this problem or something similar? Its hitting the floor pan so :S.
 
knocking sound

Just wondering if you reinstalled on old Spring insulators for the front struts, i know of someone that had this problem and thats what it turned out to be, i know Maximum Motorsport sells new ones for rougly $30.00.. Hope this helps