Basically called it right @ boogers. Happens when material builds up on the outside of the nozzle and gets deposited when it gets to a certain size or the head changes direction. You could try adjusting/lowering your extrusion multiplier; also make sure you are setting the correct filament diameter from the supplier - 1.75 mm is the standard spec but it can vary, eg. 1.72 mm.
It also makes a difference what nozzle you have to prevent buildup - a hardened & coated nozzle in a silicone sock is going to greatly alleviate that compared to just a generic $1 brass nozzle from amazon.