Ok, I may have a temporary solution here.
I own a Galaxy S Advance and have your exact same problem: audio_out2 is incredibly high, even when the phone is mute, even whit every possible sound (touch and lockscreen) disabled.
BUT the problem disappear as soon as I change ringtone. After that you can change back to the one you usually use.
From that point, at least for me, audio_out2 start working normal again.