Scraping sound from under the needle plate. That metallic grinding noise that makes you stop sewing immediately to check what is being chewed up inside. Over fifteen years of repairs, I have narrowed the culprit down to three possibilities. I will walk you through them from most common to least, and from quietest to loudest, so you can diagnose the problem without taking the machine apart more than you need to.
First and most common: the feed dogs are scraping against the underside of the needle plate. This happens when the needle plate is slightly loose, warped, or not seated correctly. Remove the needle plate (usually two screws, sometimes four), clean out the lint underneath, and reseat it firmly. If the plate has a raised lip or burr on the underside, file it down with a fine jewelers file. Also check that the feed dogs are not bent. A bent feed dog tooth will catch the plate on every rotation and make a rhythmic scraping sound that speeds up as you sew faster. If the feed dogs are bent, you can sometimes straighten them with pliers, but replacement is the proper fix.
Second most common: the hook assembly is scraping against the needle plate. This produces a deeper, more metallic sound than feed dog scraping. It usually means the hook timing is off or the hook has shifted in its mount. Remove the needle plate and bobbin case, then turn the handwheel slowly. Watch the hook tip as it passes the needle. If the hook is touching the needle plate at any point in its rotation, it needs to be repositioned. On most machines, the hook sits on a race and is held in place by a retaining ring or screws. Loosen those, center the hook, and retighten. This is a delicate adjustment—if the hook moves too far from the needle, the machine will start skipping stitches.
Third and rarest: something is physically stuck under the needle plate. A broken needle tip, a pin (yes, I find straight pins under there regularly), a screw that came loose, or even a buildup of hardened oil and lint can create a scraping sound. This one is easy to diagnose because the sound will be intermittent and irregular—not the steady rhythm of feed dogs or hook scraping. Remove the plate, look with a bright light, and fish out whatever is in there.
To diagnose by sound alone: a quiet, rapid clicking indicates feed dogs scraping. A slow, heavy grinding indicates hook contact. An irregular scraping with occasional sharp noise means something is stuck. Start with the simplest fix and work your way up. Nine times out of ten, it is the needle plate needing to be seated properly.
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