I am trying to quilt a dark fabric with clear monofilament thread. I took the spool off the spindle and put it in a cup. It sits a little behind the machine. So I was going along and the machine stopped and I had a message to recheck the upper thread. I rechecked the thread and it was fine. I started again and within two minutes the same thing happened. It sounds like the bobbin is grinding. I checked the bobbin. It was fine. I had just cleaned it, so that wasn't an issue. Any suggestions?