Admin wrote on 08.01.2017, 19:25:31 (10 months ago)
Did the phone always do this when connected to your car Alpine unit or has it just started ? It's possible that a change in phones connecting to the unit may be the cause. Check that no-one else in the car that sometimes connects is connected by disabling their Bluetooth on their device.
Also check under Settings - General - Accessibility - Call Audio Routing on the iphone. A default audio setting in this setting screen may not be on the correct value.