I have an Edge 810 and a Varia RTL515. I have four bikes that I use for training. The sound notification on the Varia only works on one specific bike. Everything else works. When I put the Edge 810 and Varia RTL515 on any of the other bikes the sound notification does not work. Can you help me solve this problem. As far as I can see the 810 and the Varia only talk to one another and are not bike specific. What's up?