You might need to try a new needle. There is often a very small burr you can't see readily. Needles do wear out, as well. Or there might be one on your bobbin case. I had that happen with my Bernina. I have not done at all well with Coats and Clark threads, however. I usually use Signature or Gutermanns. I have only tried Aurofil once, although several friends recommend it. That particular spool was a dud, which I am told is not at all common. I just replaced my Janome 1600DP with a 6600. I have been very happy with both. By the way, it also occurs to me that lint anywhere can lead to thread breakage.