Info received from another member. I took the SD card out and straight away it stopped rebooting. I can still use the hands free and music functions although not the maps obviously. I tried copying the card to another SD card but it wasn't recognised and cleaning the contacts on the Mazda card didn't help so either the data is corrupt or the card is damaged some way. However I can live without it and will maybe try updating the latest maps programme when I get time.
