I had this happen when I was a beginner. Not sure if this is what fixed it, but I wadded up a small piece of batting and placed it in the arm where the thread passes first right off the cone to keep the thead from flapping around. That seemed to solve it. The thread is traveling at such a high speed, it can get a loop in it, I guess. Try it, it might work. Maybe speed up just a little too and make sure our tension disc is cleaned out of any lint. It is mostly trial and error with these longarms.