As you may know, repetitive Behavior is one of the main characterisitc of autism. I recommend that you work with your son's school and other service providers to encourage the development of play skills that will provide alternative sources of stimulation. If your son is engaging in repetitive behavior that is unsafe or interferes with his learning, I recommend that you gently interfere with the behavior and encourage him to play a different, more appropriate way. You may find it useful to identify a local Board Certified Behavior Analyst to help with developing a plan for addressing this behavior. The website of the Behavior Analysis Certification Board (bacb.com) has a list of professionals organized by state.