Are you absolutely sure you have the correct bobbin in the machine? This problem can be caused by using a bobbin that is not correct for the machine. If the bobbin is the correct one for the machine, examine it closely to make sure it is not distorted. Sometimes even new bobbins are out-of-true. Other causes for a bobbin to become distorted include dropping on the floor, over-loading with thread (especially plastic bobbins), etc.
Googled and found the following that might contain something helpful:
https://answers.yahoo.com/question/i...0080401AAayLMK
Edit: Oh, is this problem occurring when you wind the bobbin? I thought you meant while trying to sew.