There are a few different reasons your dog may chatter his teeth after licking himself. The first possibility is that he's trying to tell you something. When dogs want to communicate with their owners, they often use body language. Chattering his teeth is your dog's way of trying to get your attention.
Another possibility is that your dog is experiencing a medical condition called ptyalism, which causes excessive saliva production. This can be caused by anything from allergies to medications. If you think this might be the case, take your dog to the vet for an evaluation.
Finally, it's possible that your dog simply enjoys the sensation of licking himself and then Chattin his teeth afterwards. Some dogs just like the feeling of having a good tongue bath! If this is the case, there's no need to worry - just enjoy watching your pup enjoy himself!