Kenda clicking....

Install a different tire and try it, I would suspect the noise is still there.

Valve stem screw (the one that holds the valve in the rim) or the piece they put in the rim to weld it together has come loose.

The first is an easy solution, the second one can be fixes a few ways; I have oozed hot glue in there before and managed to get the piece to stick in place.

lemme ask the obvious... is there a rock , nail or any other foreign objects just off center of the tire?? (ie where a lower pressure would increase the contact patch area - and thus make something like that contact the ground)

Thanks for the suggestions guys. The first thing I checked were the tires, they are perfect. I even checked the bead really carefully and even the tubes. The noise is definitely coming from the back end. I pumped up the tires one at a time and the noise went away when I got about 40lbs in the back. I switched front and back last night but haven't ridden the bike yet. Funny, I thought of the valve stem lock nuts just last night, which seems kind of obvious doesn't it; the noise has only been driving me nuts for almost a month now! I'm hoping it's not the rim, which I actually looked at with a magnifying glass. The rim joint looks ok too, but maybe that piece is loose, who knows. I guess I'll find out when I ride today.

Drew