I'd say to try a larger needle. What size are you currently using?
I would also suggest cleaning your machine. It always amazes me how much lint gets into my machine from free motion quilting. :roll: I am pretty diligent in cleaning my machine, but nothing beats taking it in and getting it done professionally from time to time. If it's been a couple years, you may want to have your machine serviced, just to be sure there isn't an underlying problem developing.
I've only just begun to learn to machine quilt myself so I don't have the experience to give any other advice. I'll be watching this thread with interest to see what the experts in machine quilting suggest.