Two things I noticed just recently, like the last two days.
When on the navigation map (I forget if Waze or Google map), turn the volume knob of the dashboard and it will lower the nav volume. I use Android Auto, not iPhone. But this doesn't remember the setting. So you may have to do it each time you connect your phone.
The big second change I noticed is that my default Nav guidance volume default setting of 4 seems to be sticking now! Even when letting the truck sit overnight. This seems new and makes me wonder if there was a software update that came automatically somehow over the air?
The strange thing now is that even with the nav guidance volume staying at my setting of 4, it still seems LOUD, but if I go to the nav guidance volume setting and bump it up to 5 (or down to 3) and then back to 4 again, then it seems like the proper softer loudness again. I still have to do more testing to see if this is something real and easily duplicated.
It's almost like after a cold start the system doesn't know the default volume setting was changed from 15 to 4 until you toggle the setting.