put music on continous play all night long the same CD. You can buy a CD player that will do this.
Put a fan on also.
Make his room really dark - I suggest putting up black felt over the windows. Buy some felt that is at least 12 inches wider and taller then the window. Attach the scratchy part of some self adhesive velcro to the window frame. The felt will stick to this velcro really easily and you can take it down easily too.
I bet those three things will make the issue go away.
Also, for a child 9 hours a night, even if they are getting 2 naps during the day, that is not enough. The average child needs minimum 10 hours a night, most need closer to 12.