Adjust the pressure of the feed rollers to the wire you are using. Excessive pressure can cause dust and thus contamination, erosion and deformation and, in the worst case, change the shape of the wire. This affects the straightness of the weld seam and can lead to a burnt contact tip. If the pressure is too low, burn-back can occur, resulting in uneven feed.
As a rule of thumb: Slight rippling on the wire surface is OK - crushing or chip formation is a warning signal that the pressure is too high.