Cats are clan-like creatures that fight for domination within their domain (known area). Your cat is demonstrating all of the signs of wanting to mate. However, that is not usually how a fixed cat will behave. Check him for injuries or slivers in between his claws. I would also check his stool. He may have ingested something he should not have. Strings, ribbons, and plastic are very attractive to cats, and once they have them in their mouth, they can't let go of it. Swallowing is the only way. If they have swallowed a string, it could be dangerous because they can get caught and cut into the digestive tract. If you can't find anything simple, you might want to take him in to see a vet just to be safe. Hope this helps.