I've had this problem crop up randomly too. Usually it's too full of a bobbin. I unload some and it seems happier. Also, try a different bobbin - if that doesn't fix it - try different bobbin thread. Of course, if it takes oil, take everything down and oil it up real well. I feel your pain though. The only time I can sound like a sailor is when my machine starts doing weird stuff - it makes me so furious. Of course, I'm really only furious that I can't figure it out. Oh - also try turning it off and back on too.