On YouTube there is a video for machine repair and maintenance. I would check there. Could be the bobbins aren't set in just right. I saw on the one where there was the teeniest piece of lint caught in the bobbin. The guy took a very tiny pin and picked it up. My fairly new machine was making an odd noise (starting to clack) so I tried his tip. No more clack. It was a tiny piece of lint smaller than the width of a strand of hair.