I have a Juki DX-7, which is in many ways similar to the F series Jukis. My machine made this same rubbing/scraping noise after only a few months' use. Even though the operating manual has no instructions regarding oiling, I was advised by a member here on QB to remove bobbin and bobbin case, and apply oil around the small metal circle under the bobbin case. It did the trick, and I now oil that area regularly. It's very unfortunate that Juki has not included that information in the manual.