Problem with bluetooth

Many people including myself have a problem when our iPhones are connected to Bluetooth for hands free phone calls while driving - our message notification alert as well our gps navigation voice are both silent - when we disconnect from Bluetooth both navigation voice & message alerts sounds are working - & all our settings are on & correct obviously as the gps navigation voice & message notification alert ringer is working when we disconnect iPhone from Bluetooth - But this is something I do not do as we lose our hands free phone call ability -this is a problem - glitch between iPhones & Bluetooth - no one seems to comprehend or grasp this problem - many so called “experts” continue to advise us to go to settings to troubleshoot - Follow along now gang - when iPhone is NOT connected to Bluetooth , message notifications & gps navigation voice both work - when connected to Bluetooth they are both silent - therefore settings is MUTE - Why does Bluetooth eliminate the navigation voice & message notification ?