What might have caused this off flavor?

This was my first partial grain biab, version of Jamils choc hazelnut stout.
The LME was added 30 min into the boil.
It was a full boil, and coolled by putting the kettle in an icewater bath (took about 50 minutes to cool). Pitched a 2L starter of wyeast british ale ii at 67degrees.
Going into the fermenter, it was slightly more bitter than i expected, but otherwise tasted like wort.
13 days later, it was done fermenting, and i tasted my FG sample before racking into the bottling bucket. It has what i can only describe as a metallic flavor, which definitely wasnt present before fermentation. I used a stainless brew kettle, and an ale pail fermenter (sanitized with star san). I went ahead and bottled normally, but will the flavor change during carb/conditioning? What might have caused this, so i don't repeat the mistake?

The flavor will change after the beer bottle conditions and such, so I wouldn't put too much stock in to it until you taste the final product. I do however have a couple of questions/comments:

How's your water? Does it have a really high iron content? Water is much more important in AG/PM brewing than in Extract brewing.

How old was that can of LME? LME in a can can give your brew a metallic off-flavor. I only use DME, it's more potent per lb., stores easily, and stays fresher much longer than LME.

John Palmer said:

Metallic flavors are usually caused by unprotected metals dissolving into the wort but can also be caused by the hydrolysis of lipids in poorly stored malts. Iron and aluminum can cause metallic flavors leaching into the wort during the boil. The small amount could be considered to be nutritional if it weren't for the bad taste. Nicks and cracks ceramic coated steel pots are a common cause as are high iron levels in well water. Stainless steel pots will not contribute any metallic flavors. Aluminum pots usually won't cause metallic flavors unless the brewing water is alkaline with a pH level greater than 9. Shiny new aluminum pots will sometimes turn black when boiling water due to chlorine and carbonates in the water.

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The protective (grayish) oxides of aluminum can be enhanced by heating the clean pot in a dry oven at 250°F for about 6 hours.

It's a farily new stainless brewpot, and other batches didn't show this flavor, and the flavor wasnt present after brewing, so I'm comfortable ruling that out.
The water has never exhibit rust or off flavors.
The LME was bulk from AHS, purchased this month, it came in a plastic pail, so really doubt that was it. Plus, the flavor developed after fermenting.
I'll post again in a few weeks with a flavor update.

It could just be a byproduct of the fermentation, I'd just let it sit in the bottle/keg for a while and see what comes of it.

On a more positive note, I just racked my marzen to secondary and stole a sample to check gravity, and it tastes really good already.