I have the same or a similar problem, but only when I'm using Bottomline thread in top and bobbin. (I like to do that when I'm piecing.) I haven't asked my dealer about it, since I have been assuming that the thread is the problem. The thread doesn't usually break (although sometimes it does), but it looks like the needle is picking up extra thread from the bobbin. The machine makes a funny noise, and if I stop before the thread breaks I can see that extra thread and can even cut it and then continue sewing without re-threading the machine! This only happens when I'm chain piecing, between the two pieces in the chain. I intend to ask the dealer about it next time I take the machine in for cleaning and check-up. (I have a service protection plan, so I can take the machine in as often as I want for no additional cost.)