Hi all - I have a strange issue with the cb4500 which I don't think has been there before but I may just be going mad :D   The top thread is being picked up fine by the hook, but when it slides over the bobbin case to form the knot, it seems to snag on the little hole right at the bottom of the bobbin carrier and then snaps back up when the tension is increased at the end of the stroke. I don't think this is correct as it makes a loud snapping noise and I cant remember that happening b