I have a Bernina Activa

Question

I have a Bernina Activa 135. It will sew for awhile just great and then it starts to make a crunching sound and the bobbin thread bunches up on the underside. It will then go back to sewing just fine and then......it happens again. It even does it on the striaght stitch. I am also looking for a sewing machine repair place here in Northern New Jersey as we have just relocated here.Thanks