I have a Husqvarna and I had the same issue once. I re-threaded the machine and re-loaded the bobbin until I was blue in the face. I even took it in to have the experts look at it. As it turned out, nothing was wrong with my machine nor my threading/bobbin loading technique. It was simply the brand of thread I was using. I traditionally use the Gutermann brand but ran out in the middle of a project. I had a comparable color in the Coats & Clark line so I used that. My machine did not perform well at all and I had a huge rat's nest on the bottom of the fabric, the tension messed up and the automatic thread cutter locked up. The experts at the shop asked what type of thread I use, and suggested that the brand might be the issue. We took out the C&C, got out another color of the Gutermann to try and the machine purred again. Strange, but true story! If you've tried all of the other options you've mentioned, plus this one, and still no luck then take it back to see if they will exchange the machine for you. Best of luck to you!