Metallic thread does require special handling. What brand of metalic are you using -- the sulky thread has to lay on its side and is the only one I ever have real problems with (but only a couple of colors). When I use metallic thread, I make sure I use a large metallic needle (metallic needs to glide through the needle), I usually use a thread conditioner, I loosen the tension and I go slower than I normally sew. Other than a couple of Sulky colors, I don't get thread shredding.