My Pfaff 130 did something like this. Since you are sewing with fleece, my guess is that there is a small bit of thread or lint caught in the bobbin assembly. It may be too small to see, so get your magnifying glass and tweezers. Those bobbin assemblies are so finicky on that machine, although it is a great machine. Don't ever try using your bobbin for a decorative thread. Ask me how I know!
Cricket