another thought, if the headset ends up being fine and the sound still persists, it could possibly be the hub's cup/cones are loose? my rear hub was loose and there was some side to side play between the hub body and the axle... anyhow, it made the same noise as the headset problem, almost exactly, when i do the 6 inch drop test. but, if you feel movement when steering or hear the noise when going over bumps and such, chances are its the headset. but i'd give the hubs a once over too to check.