This sounds familiar! I have a Janome as well, and LOVE it--but it kept making weird noises and refusing to sew, even right after I had just retrieved it from the shop. I found that if I will completely re-thread the upper thread it will sew smoothly again. I did take it back to the shop again to have the needle threader aligned and the thread cutter adjusted. They cleaned and oiled it and said that the timing had needed adjusting. It's doing beautifully now, so that must have fixed it! :-)