Several things. Try inserting the bobbin you orginally took out- it may be the bobbin itself. First and formost unthread everything and clear the bobin area of any lint or threads that maybe causing a jam.
Some machines do better with metal bobbins and other plastic- you have to test and feel. The metal usually seat better and jiggle less due to their weight and smoothness.
Plastic can have tiny nicks that catch and do have a drag to them as the plastic is scratched from turning during use.
If you've tried these and still having trouble take it back to the store if it's new. If not cal Brother and talk to them.