John and Greg, et al.,
I disassembled the hub and cleaned it thoroughly. I soaked all of the components in PB blaster for 48 hours and blew them out under pressure. I soaked them for 24 hours in lacquer thinner and blew them out under pressure. I rinsed them off with WD-40. As I reassembled them I followed the lucrication guidance in the Schwinn Bicycle Service Manual. The reassembly was effortless and fast. It runs out perfectly in granny but is making metallic chattering noises in high. The brake works perfectly. On the bench, there is no resistance to rotation in either gear. There is no play in the hub/bearing interface. On the road, it shifts perfectly.
Where is the noise coming from?