I found this too along with bleeding gums being a cause. Who'da figured? I did a web search for metal taste in mouth.
There are many causes for metallic tastes. The most
common are medications however reflux can also be a
factor. Mints can trigger reflux and should be
eliminated as a trial. Sinus infections might be
another possibility.
I agree it could be what it was washed with, maybe just not rinsed out well.
