Did you ever answer the phone and sigh because you heard “the voice” of that someone you love? That’s because you had / have a relationship with that person. You have talked enough – and listened enough – to know the voice as soon as s/he speaks.
Our relationship with God works the same way.
We can know it is HIM speaking when we maintain a relationship with Him. We know the moment he speaks because we are so familiar with His voice.
Sometimes He whispers. Sometimes He speaks very clearly.
And sometimes He remains silent.
but when He speak – and He will – you will know it because you have a relationship with Him.