That is due to one of your a is vibrating while moving so check for play on both axis, if using rack and pinion check the tooth aligment and proper seating, if you hav motors directly driving pinions you will have to put in reduction or use quality microsteping drives. If you have to much distance betven the x axis rails and the torch head try puting something under the sheet and do a cut as high (near the rails) as posible.