I've been trying to track down this major annoyance.
I went to the dealer, they are no help. They say that they checked and all vehicles do this, so it's not a problem with my BigHorn. Yes of course, it's a firmware/software problem in all units! LOL I guess their mindset is that if my truck is the same as others, then it's ok and working properly! LOL But this is a separate issue as this dealer doesn't seem to want to look into issues of this type (I have a list of several things like this).
When I first got my truck in January. and up until approximately two days ago (plus or minus, as I don't check this every day) the Nav Guidance Volume level setting would always default to 15. This is MUCH too loud! If you try to set it to a lower volume level (I find that 4 to be about right with the windows closed, it's not to soft, but loud enough to be heard over traffic and music), the setting would not hold. After starting the truck after it sat a while with the power off (about an hour, or over night), the Nav Guidance Volume level would reset itself to 15 again.
Now as of a couple days ago to talk about how it's working now: The Navigation Guidance volume setting is holding at my choice of 4! I don't know why it's holding now. but it is (with limited testing). Perhaps we received a blind software/firmware update to the UConnect or system over the air? I have no way of knowing as I wasn't tracking the software versions.
But with the Nav Guidance Volume setting sticking at my chosen level of 4, BUT it's still not functioning correctly!
This is strange to notice and test. It seems to be using the volume level at the old default 15 loudness, even though the display is showing 4! It's quite loud and easy to hear. But then if you go into the Nav settings menu, choose Nav Guidance and set the volume up one click to 5 (or down one click to 3) and then back to 4 again, now the loudness of the Nav guidance is at the proper softer volume level. So it seems the actual volume of the Nav guidance voice is always very loud until you change the Nav Guidance volume level. This is hard to test as you need to notice the volume level of the guidance sound, and then click it up/down (or down/up) and then notice the change in volume.
So it's unknown to me why the Nav Guidance volume level is working differently than in the first month of me owning the truck, but it's still not implemented correctly, in that you will be startled by the volume of the Nav Guidance.
I test it by setting the Speed Limit warning on. You can set to give a warning at or above/below the posted speed limit. Under normal use, I keep this speed limit warning set to +10 MPH over the speed limit, but during testing you can lower this and cause the Nav unit to talk almost on demand by speeding up or down. LOL
I have the 8.4 display with Nav and the standard 6 speaker 'radio' (NOT Alpine nor HK) on the Bighorn.
Sorry for the long post, I'm trying to provide as much info as I can on this frustrating issue.
Is anyone else seeing this?