you are talking about the two snaps for the Map case? Inside the snap is tiny metal ring that tensions the snap, that is what is rattling. I assume you are not useing the map case because mine will only rattle when there is no map case attached. If you are never going to use a map case you can dab some latex caulk or silicone in there.
If you want to be able to use the Mapcase at some point . take the bag with you to a hardware store or Fabric/craft store and get the male button that fits the snap on your bag.