Janome MC 4000 obbin rotates past the spring

I'm the only owner of my machine and has always taken care of it. Suddenly when I sew, I hear a loud knocking noise. And, this only happens once my bobbin case shifts. I still have good straight stiches, but is unsure if my decorative stitches should be distorted on the bobbin side. Once I check my re-threading, needles, lint and tension, I look into the bobbing case and notices that my bobbin case has spun past the spring, but not enough for my needle to hit the case. I've recently had my bobbin case replaced during pro maint. Now, I'm not sure if this should be happening and this spring is what actually keeps my case locked in place during sewing. But, this seems to make the noise more apparent. Again, I've already had it serviced and oiled and everything checked out, so what next? Thanks!