Practice first always...but...from what you say...rethread the top thread. I swear my Singer does this so often...that I will thread it and then do a practice swatch just to be sure. 9 times out of 10 I get those little loops on the bottom. I finally (after MUCH work and frustration!) learned, to always do test first as it will almost always be just a thread problem! Un thread completely and then rethread and try the test again. I have found..it works out every time!