I've just spent quite a long time struggling to start some FMQ because of an issue with either my machine or my technique - not sure which. I start to sew, and immediately there's a "clunk" and I have to stop straightaway as there'll be a birds nest on the back of the quilt. It's happened before and I can't work out what causes it - once I've got going, the machine sews quite happily. I've checked that the pressure foot is down and that all is correct with top and bobbin threads and the bobbin case.