Hi, I was out riding yesterday, completed 60k no problems, all of a sudden my Shimano Di2 rear wheelset automatically shifts to the smallest cog and stays there. It does not respond to any gear changes. The battery works fine as the front derailleur works fine. Each time I flick the gear a whirring noice comes out from the central box. Any suggestiosn as to whats wrong, I removed all the electronic connections and re-connected without any luck. Kerry