Too late to help with your enquiry, which I'm glad to hear you have resolved, although did the factory reset cause you to lose any addresses etc stored in your navigation? I had a similar problem with my sat nav audio recently - there was sound but it was very faint. Wasn't initially affected by the radio volume, but I eventually found out that I had to alter the navigation volume while it was giving directions. I think the problem was caused by turning the radio volume down at some point, and I must have done that while it was making a navigation announcement.