I have an odd problem (as usual). I set my guidance volume at 11. A few weeks later, I notice that it's getting very hard to hear the voice prompts, so I check the setting and it mysteriously shows the guidance volume set at 3 or 4. I haven't made any changes. This has happened repeatedly. I am the only driver of this car and only use the key labeled "Driver 1." Any ideas about what is happening? And how to make it stop changing by itself?