Q: iPhone 6s keeps connecting to car Bluetooth thinking a call is being made

II've noticed over the last few weeks (possibly since the iOS 10 update, but not sure) my iPhone 6s will often connect to the hands free Bluetooth in my cars and think that a call is being made (as indicated on the car), but no evidence of a call being made on the phone. It seems to happen very regularly with one car (2015 Subaru Outback), where it will connect as soon as I get in the car, be difficult to disconnect, and often reconnect again shortly thereafter. In this car I am often not using Bluetooth to listen to music at the time. In my other car (which has an aftermarket Pioneer Appradio head unit) I also set always have the phone connected to listen to music, but on short trips where I don't hook it up I have noticed this same issue (the radio thinks I am making a call).

Any ideas?

Thanks,

Joe