How do we know when God is speaking. Most of us are filled with confusion concerning this. An encounter with His presence makes you different, it is more distinct than anything else you hear and/or perceive, it's more intuitive.
Discovering the voice of God is a divine mystery because it is supernatural through the Holy Spirit. There is no formula or scientific data to which you can confirm or discern it, but His voice is 100% accurate.
Practice the discernment. God allows our errors to be our teacher in hearing Him correctly. Challenge your anticipation to hear from Him. Get into your quiet time. Open your heart to the leading of the Spirit to teach you the way. It will break through many barriers, (Discerning The Voice of God/Priscilla Shirer, 2006)