"Klunking" sound when sewing

Question

I am a new owner of a Pfaff Creative 7570, which I inherited upon the death of my sister. I am sewing terry cloth and it started "klunking" while sewing. I cleaned around and under the bobbin, also oiled where it shows in the manual and changed needles. However, it still continues to "klunk". Can you help? Thank you.
Mary Weiss
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