Metal flavours. The bane of my existence.
I've experienced them HEAPS in commercial beers from HEAPS of different breweries. And then I has one of my brews display it.
I've heard a number of different reasons as to what causes it. But mine that I've settled on as making sense in being in all the different beers I've found it in, maybe it wasn't the one single cause.
I've heard: too much dry hopping, too much Amarillo, poor storage of beer (which I lean towards, i.e. warm, cold, warm), too many minerals and a host of other reasons/possibilities.