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.

Did you pull the bobbin thread to the top ???

Try bringing your bobbin thread up before you start. When you are ready to FMQ, take one stitch (or use your hand wheel to put your needle through your fabric and then turn it till you bring the needle back up up). This will bring your bobbin thread to the top. Pull the bobbin thread and your needle thread under your presser foot towards the back of the machine. Then start your FMQ. That should eliminate the birds nest on the back.

And if the bobbin thread has been pulled to the top and your holding it to keep it from drawing back with the first stitch, the presser foot is down, the machine is threaded correctly. And it's still nesting. I start looking for the following, is the bobbin in right? Any fuzz/lint in the bobbin case area? I also look for that last little thread in the case that will cause the nest.
Just a thought..

Yes, I always do pull the bobbin thread up before I start, so it's not that...

Taking out the bobbin case and cleaning it does sometimes help, but not today. The weird thing was that it happened almost every time I started sewing the actual quilt, but not nearly so much on the practice piece (same fabric and batting), so I did wonder if maybe it was something to do with my technique as I started, maybe being a little less relaxed when it was the quilt?

My machine makes a "clunk" sound when I lower the feeddogs. Could this be what it is? If it is just when you first start, perhaps the feeddogs are not completely dropping until you start to sew.

needless to say....feeddogs are down....
and yes...take a couple straight stitches before you start
the quilting.....

are you holding onto your bobbin thread so it does not go back down thru the quilt....quilt very slowly in the beginning....

Is this that troublesome Janome AGAIN?!!!! I'm sure there must be a problem - get it serviced by a Janome approved engineer then book yourself in for some lessons. These problems are apparently unsolvable by online advice from any forum. :?