For most Gibson style pickups, make sure you are using a quality height adjust spring. It's a compression spring and has a fair amount of pressure to hold the pickup firm. I also use a piece of foam rubber to help keep the pickup from moving around inside the pickup cavity. On Fender style pickup, I would make sure you have the proper height adjust spring and adding either a longer or firmer piece will usually do the answer. I find that Gibson makes the pickup cavity with pretty close tolerances so the pickup should not rock back and forth too much. But again try using some foam rubber under the pickup. This will help and also reduce a little acoustic feedback.