What stitch length are you using? Needle plate? You might try the straight plate if you have one.
What foot are you using? There is a foot (1/4 inch with guide) with a black button on the side that allows the foot to raise a little so it can go over bulky seams. Not sure if it available for your machine.
It may also be the way the intersections are going in to the feed dogs. Try the bottom seam pointing towards you. Top seam pointing in to the machine. Good luck!