How to fix small loops of bobbin thread when using a Singer Prelude 8280 machine?

I recently got a used machine, and it has loops of bobbin thread on the bottom of the thread no matter what I do. I tried all tension settings, even up to the highest, and still have loops of bobbin thread. I re-threaded the top thread, with the presser foot up, double checking to make sure it's right. The bobbin is threaded correctly and all the parts are inserted correctly. I dusted out the machine. And I STILL have loops of bobbin thread on the bottom! I used two different colors of thread, so I know it's the bobbin. The loops aren't big, only about 2-3mm or 1/8 inch, and aren't tangled.