Not sure if it is the same problem, but my Singer 9960 ..I iwll be FMQ'ing and it look perfect on top, no noise, just sounding totaly normal and then when I check the back just to check for quality stitching...I see the pattern I stitched is TOTALLY "bird nesting" the entire length I sewed! I can't understand how the top is perfect stitching, but all that thread on the bottom..where'd it come from and why so much ont he bottom and not the top? It is one of those "oh well" things...but to fix it... I found out it was my TOP thread causing the bird nesting. I simply unthread and re-thread the upper thread. Might take 2 times, so it must be something inside the thread track that doesn't click or get hooked or something, but..it solves the problem...I start sewing and t he bottom stitching is good as the top! I also found that if I have cotton in the top and poly thread in the bottom (or visa versa) it will do nearly the same problem stitching...so I always make sure I have same thread top and bottom and that problem solved. I guess the poly is slippery on the cotton so they don't join well. GOod luck, share your solution!