It sounds like you've used the attys and cleaned them often enough to get rid of any primer fluid that was on them, so I don't think thats it. I think you should try changing your filler material like Dormouse said. Don't throw your carts away, just pull out the cottony filler thats in them now and go buy some blue aquarium filter foam from the pet store. Cut a piece sized to fit in your cart with just a slight compression (this is the Blue Foam Cartridge Mod) and push it into your now empty cartridge. I also use the straw mod in combination with this but you don't have to. Look it up in the cartridge mod section of the forum. OH! I just remembered something VERY basic! I haven't used the stock filler material in so long, I forgot. Those cottony fibers can get stuck to the wire mesh of your bridge and taste very burnt! You MUST get a magnifying glass because they are hard to see, and look if there are any stuck on there then pull them off with a pair of tweezers. Oh man, I bet that's the problem! Let me know, ok?