Did you add any meat to it, or was it just bones and veggies? I've found that pure bone stock is kind of musky. I've had much better success when I've added meat as well.
Also, did it ever come to a boil? Think of it as steeping tthe bones/meat/veggies in 180*F water for a long time. It gets icky if it boils. Also, did you skim the protein scum from the top? That can make it icky too.