If you don't want to pay $7.99, you can just open a terminal and type:
>defaults write com.apple.BluetoothAudioAgent "Disable HFP" -int 1
>defaults write com.apple.BluetoothAudioAgent "Disable HFP" -int 1
When I connect my headphones and switch to the microphone, the same crappy sound comes up. I had tried before with the checkbox in the bluetooth explorer to disable HFP, but also didn't work.