Mike,
The first suggestion i would make would be to check your bearing edge. As with
any drum, the most typical cause of unwanted high-frequency overtones is bad
contact with the head and drum. This applies to any kind of head.... synthetic
or skin (however, the thinner the head the more the overtones that exist,
typically).
I would recommend taking the skin off and examining the bearing edge for gouges
or rough spots. Even just a little sanding might help the sound considerably.
--Dylan Fila
Sunrise Djembes