Hi kk107 and Welcome to the Board. I'm Laura and I'm the furmom to a 14YO dalmatian, Samantha and 3YO lab/mix, Cleo.
I've never heard of this before, nor have I ever seen this behavior with any of my dogs. Your dog is young, and if he is getting enough exercise then I don't see why it would be a boredom problem. However, it may be a neurological problem, and only your vet can advise you on that.
I hope that it is just a "habit" that he has....and nothing else. Please be sure to let us know if you take him to the vet, and what he tell you.