Media audio to 3.5mm cable, while using Bluetooth for phone calls...

This is a common problem with newer Samsung Galaxy phones, like the S3/S4 as Samsung has changed the default audio output from Bluetooth media to Wired headphones.  This means when you have a Wired headset, or 3.5mm cable plugged into the phone going to your car, the phone call audio will also go through the 3.5mm cable to your car's AUX input.

SoundAbout will change the default audio output back to Bluetooth in the Bluetooth behavior category.  
There is a setting called "Phone call usage" that sets the default phone call audio to Bluetooth mono when the SoundAbout Phone call audio setting is on "Let app decide".
There is a setting called "(A2DP) Media audio usage" that sets the default audio to Bluetooth media when the SoundAbout Media audio setting is on "Let app decide".