A classic from Bill MacKinnon: No Voices in My Head
Update– This is my favorite bit, and it hit me like a 2×4 when I first read it a few years back:
It is curious to me that if someone in a typical evangelical church stood up and said an angel spoke to him and told him that God wanted him to be a missionary to Africa, we would be very skeptical at best. Yet if that same person stood up and said that he “just really feel led to go to Africa to be a missionary”, the “amens” and applause would be deafening. Yet the former is biblical and the latter is not.
Kirk Cowell 
I agree with you that we should be aware of what God’s voice actually is. Here is an illustration of two different views.