Since nobody else has responded yet, but several have viewed your question, I'll take a stab here.
I don't believe you will find it "usual" for someone with MS to complain about a metallic taste, but I'm sure it's not unheard of. BUT, having said that, I would still mention it to your physician, as that could be a sign of several different things (including a side-effect from some medications).
I did find an article that you may find interesting, and I'll paste an excerpt from it here. You can find it at: http://www.webhealth.co.uk/WebHealth_A- ... neral.html
Q: What does it mean when you have a "metal" taste in your mouth that is persistent?
A: There are many things that can distort one's sense of taste. Change in our ability to taste can be a very unpleasant sensation as well as a signal of other health concerns. ...
...Once the tasted item hits the taste cell receptor, there is a change in the cell membrane, causing a flux of ions through the membrane and stimulation of nerve endings, which in turn send signals to the brain for interpretation and integration. A lesion or problem anywhere along this pathway can muck things up. Therefore, inadequate saliva; the destruction or coating of taste buds by infections, toxins or other problems; and injuries to the nerves or brain all may cause a reduced or abnormal perception of taste. " ....
I hope this helps some. I'd advise you to perhaps take a look at the article, and at the very least put this symptom on your list of things to discuss with your doctor the next time you see him/her.