"Stepped" Prints - Take a Look

[Phantom462]

Hi guys, can someone take a look at these pics of my print and give me an idea of what is going on? It doesn't always happen at the same height nor does it have any kind of pattern. Some prints it happens, some it doesn't...the same print. I've replaced the stepper motor and re-flashed the firmware, the belt is not slipping... I'm kinda at a loss.