One thought I have is, do you have the correct FMQ foot on your machine? It needs to set a bit above the plate (when you have the presser foot down), so the fabric can move smoothly under the foot as you are sewing a design. Also, your needle may be pulling the fabric down as you sew and you feel a catch each time it drags the fabric into the needle plate. A single hole needle plate helps with that problem if you have one, rather that one that is used for a zigzag stitch.