Did the metal taste come on with menopause? I ask because some women have a metal taste in their mouth when pregnant, presumably related to hormonal change. Possibly you could get your hormones checked, and if they are way out of balance to the normal proportions in the body, maybe get a light dose (I'm not talking about hormone replacement therapy, but something very light and only for this purpose) to see if that what it is. Your doc would have to be sympathetic to this experiment, because hormone replacement therapy is controversial, supposedly doing more harm than good.
I do not want to scare you but look at the Chiari Malformation board. There could be a link there.