Manual Uninstall

Delete Background Music.app from /Applications.
Delete Background Music Device.driver from /Library/Audio/Plug-Ins/HAL.
Pause apps that are playing audio, if you can.
Restart coreaudiod:
^{(Open /Applications/Utilities/Terminal.app and paste the following at the prompt.)}
```
sudo launchctl kickstart -kp system/com.apple.audio.coreaudiod
```
or, if that fails
```
sudo killall coreaudiod
```
Go to the Sound section in System Preferences and change your default output device at least once. (If you only have one device now, either use Audio MIDI Setup.app to create a temporary aggregate device, restart any audio apps that have stopped working or just restart your system.)

Optional

Delete BGMXPCHelper.xpc from /usr/local/libexec or possibly /Library/Application Support/Background Music.

Unregister BGMXPCHelper.

If you're using OS X 10.11:

sudo launchctl bootout system /Library/LaunchDaemons/com.bearisdriving.BGM.XPCHelper.plist

If you're using an earlier version of OS X:

sudo launchctl unload /Library/LaunchDaemons/com.bearisdriving.BGM.XPCHelper.plist

Delete BGMXPCHelper's launchd.plist.

sudo rm /Library/LaunchDaemons/com.bearisdriving.BGM.XPCHelper.plist

Delete BGMXPCHelper's user and group.

sudo dscl . -delete /Users/_BGMXPCHelper
sudo dscl . -delete /Groups/_BGMXPCHelper