Typically what most use for break in is minute rice, or a knock off.
You can also go with grinder cleaner, grindz or which ever other brand has the pill shaped stuff. Joefrex has a cornmeal based powder IIRC.
I've had the EK for a while and don't remember a metallic taste, so hopefully something like this will help you get it right. I suppose if you're really curious you could hold a powerful magnet over your ground coffee (or stir the grounds with it) and see if it collects anything. Assuming any metal that could be coming out would be magnetic. That's a lot of 'ifs' but I like experimenting myself
Good luck, you'll be fine once it has broken in no doubt.