Harmonic sound whenever I played 12th fret? How to mute?

So I learn ‘Sweet child o’ mine’ by GNR, I heard a harmonic sounds whenever I release D on 12th fret whereas not as much sound when I played G on 12th fret.

Is it normal? Is my speaker too loud? should I mute it? how?

Here’s a link to video of me playing: swee child o mine

submitted by /u/mydesktopissquare
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