Ok I don't have children of my own yet, so this is strictly my opinion (with bits and pieces from being a big part in the lives of 10year old twins - 1 boy 1 girl)
He started doing the same around age 7-8 progressively getting worse, and we found the only way we could kerb this behaviour was to essentially bribe him... we would take time off computer use / nintendo ds / playing with pets etc what ever it was that he was greatly interested in at the time. It can become hard - he would say he didn't care if we took that time away from him and would continue the behaviour, but we persevered and now, almost 10, he seems to have learnt that the behaviour has consequences that aren't beneficial to himself IYKWIM
As suggested though, I would get his hearing etc checked just to make sure...
Good luck and hopefully it is just a phase