Could be any number for things but first check all your connections to Autocom jack leads - if they are even slightly disconnected then the feed will default to the units speaker.
Check the Autocom AND the Satnav are fully powered - might also want to check in a car mount to make sure the mount recognizes the unit (it should shift between a car icon and a bike icon)
If all that is OK then some have experienced a poor connection on one of the contacts which means that a new cradle is required - if the unit is in warranty no probs - if not its cheaper to buy a new mount off ebay or amazon>
Regards
Rik