But it's probably not. Over carb, for me at least, does sometimes produce metallic flavors. Some things to check: how old was the keg (usually have the date stamped on the label near the coupler), check to make sure your regualtor is really on the right setting (although if it was higher the beer would be gushing out when you open the faucet) Another likely culprit is that new kegerator taste
, sometimes happens with brand new kegerators (you say its the first keg) especially with chrome faucets and shanks. Try flushing the lines, and cleaning with BLC, and hot water a few times (Dont forget to dissassembly and wash the faucets too, and sankey couplers) then flush with cold water before trying the beer.