On Will and Grace, when Grace was on her first date with Leo, she asked the same question and he asked her if she keeps her mints in her coin purse.
On a more serious note, my mom associates this taste with the taste of blood. I believe that would be a sign of gum disease which she suffers from.
Do any of you prescriptions list this as a side effect? Might want to ask your dentist and your pharmacist about it.