Funny you should say that Spring - we listen to metal in this house and he does head bang along with it.. haha!!!!

Umm... I think it lasted from about 14 to 15 months to.... maybe 20 months? He hasn't seriously done it for a while - will regress now and then and do it once or twice a month I suppose... now he just shrieks at the top of his lungs if he wants something.. less painful for him.. more painful for us!!!!