metallic rap one per wheel revolutiom clutch in or out, disappears under load

I've got gear rattle on decel, and this sounds different.

With the car moving, can hear a a higher pitched metallic tapping noise in time with the revolution of the output shaft side of the drivetrain. Happens with clutch in or out, and disappears when the transmission is under anything more than very light throttle application.

Also sounds like it is back farther than the actual transmission, in the shift linkage/center diff.

I've read most of the center diff bearing issues and the sound really doesn't match, but I figure that's the first step? Any other possibilities?

Thanks!