I would give the machine a good clean. I would floss my tension discs and clean and put a drop of oil in my bobbin case if your machine allows that. I would check the thread path going to my tension discs to make sure the thread is not catching on anything. What kind of spool of thread are you using? When I use a cone of thread behind my machine, it occasionally will wrap around the extra spool pin on my machine causing a mess. Stacked thread on a spool likes to feed from an upright spool holder and cross wound thread likes to be on a horizontal thread holder.