Jenn, I posted this same problem a few weeks ago. My fw had been sewing just fine and suddenly the thread started winding around the bobbin assembly. Nothing I tried worked, including taking the whole assembly apart, cleaning it well and reassembling. Finally took it in to the repair shop. He told me that the inside of the bobbin area has microscopic scratches that catch the thread - caused by lots of reasons, including bad bobbins, and sometimes just age. He polished it and now it's working just fine. But he told me it's a temporary fix and will likely happen again so he didn't charge me. You can find instructions for fixing it yourself at
www.tandtrepair.com
Good luck, it's worth a try.