hello. i have been having a problem lately with my straight stitch coming out wavy looking. its only on one side and not constant. i have changed fabrics and rethreaded. i'm not sure if its a problem with the machine, or thread, or the way i'm doing something. here is a scan of what it looks like. i couldn't get a picture because my camera kept focusing on the pattern instead of the stitches. any ideas?

also, is this problem going to result in low quality stitches? in other words, do i need to redo that hem or do you think it will be ok? thanks for any help!