Disable end call beep

The end call beep is EXTREMELY loud when connected via bluetooth to a car or headset I haven't measured but I'd have to say it is in the 80-90 db range on my cars. Anyone know how to disable it? I've done a google search and while the question is common, the answer seems elusive. I've seen one solution that was a modified Phone.apk file. I went looking for the M9's Phone.apk but haven't found it in system/app or priv-app. Some older android version seem to have a setting option to turn it off but it is sporadic and no where to be found on the M9. Others have suggested a play store app but the app only adds an end call notification, it doesn't stop the existing one.