How do I fix my Brother cs6000i from thumping?

My 3 month old Brother cs6000i has started an irregular thumping. It seems to start it after I've been sewing for 10 min or so. If I stop and walk away, I can sew again for another 10 min before it starts up again. Is it overheating and starting the thump? I don't feel any heat on the outside of the machine. I have used different bobbins, different threads, cleaned lint out of the bobbin case and that area. It just started today, and I've been quilting, so have been sewing for long stretches. Please help!

Renee
July 2010