The Wine Spectator magazine says, regarding metalic taste in wines:
"First off, there's a difference between "good metallic" and "bad metallic." Some excellent Sauvignon Blancs and Rieslings might be described as "steely" or "flinty" (positive descriptors that are often attributed to grapes grown in mineral-rich soil). On the other hand, unpleasant metallic or "tinny" notes can come from
brettanomyces, a spoilage yeast. "Metallic" can also refer to a tactile sensation that comes from low-ethanol, dry, high-acid wines, or to the astringent feel of some highly polyphenolic wines. Also, there are combinations of both medication and food that can impart a metallic taste to wine. I've experienced this anytime I've been on antibiotics—or tried to pair red wine with sushi."
Brettanomyce is a wild yeast found on the skin of fruit. "It is thought
Brettanomyces can be introduced to a winery by insect vectors such as fruit flies."
It may come from any of, or a combination of these factors. It will go away, they say, if you let the wine "breath" for a while before drinking, or it may dissipate with some time in the bottle.