Update: Problem solved - the axle system had worked itself loose. My LBS mechanic had it tightened back up in less than 5 minutes. Kind of embarrassing since I thought I detected no play in the bearings. Once the wheel was removed from the bike the drive side spacer was visibly wobbling. I know how to service old school cup and cone hub bearings but other than watching my mechanic and reading a few articles about it and watching a few YouTube videos I still had not tackled the FH-7800 hub adjustment. I have a used Dura Ace FH-7850 that I had built into a wheel with some Velocity Quill rims and those bearings feel kind of dry. If I could ever get some real free time, I will repack the bearings on this wheel and follow the directions I found on-line.