The pads are loose, or the calipers? The calipers shouldn't be loose. The pads are loose around the bolt so that the spring will work. I've found the best way to align them is to pull the pads out, put the wheel with disk in, center the slot in the calipers on the disk, tighten down the calipers, pull the wheel out, push the pistons all the way back in, replace the wheel and then replace the pads. Then it Just Works. But until I figured that out the hard way, I had your experience. I've also noticed I periodically have to re-seat my front wheel in the fork drop-outs. Thru-axle would have been better.