That just happened to me after cleaning out my bobbin case. I was so frustrated, nothing I did made a difference. So, I backtracked and removed the whole sole plate and bobbin casing, put it all back together again, rethreaded the top thread, made sure my needle was in all the way, put In the bobbin thread, and checked the tension, which was correct already. Still didn't work! So, back off came the sole plate and bobbin case, and back together again, and I realized I didn't have the bobbin casing in correctly. It is a little tricky to get lined up just so. Now, she purrs like a kitten! DH even asked if I got the bobbin case in correctly and I swore I did! Won't do that again!