could be mounted wrong, but i would check the balance of the fan first. set the fan on low and place a washer, attached with tape on the upper side, (side you can't see from the ground), on one of the blades and turn the fan on. is the wobble worse or better. put a washer on another blade, taking the first one off, keep doing this till you find the fan is getting better. you may end up with a couple of washers on one or two blades and none on others. if this doesn't help, probrably the fasteners in the ceiling have come loose.