I may know what you're talking about. I made a (extract) brown ale with fuggles last February. It tasted, not sour, but twangy. Is that what your' tasting? It was in the smell and taste and was my worst beer to date. I wouldn't even drink it and of course it seemed to be the batch that had the highest yield into bottles. Then I put one in the fridge a few weeks ago, and the "twang" has turned into a very definite Hop flavor. It is not what I figured it would be being a Brown Ale, Taste more like a light IPA-ish Brown. But it's good now. Might just be the flavor of fuggles. I'd be curious to grab some fuggle pellets and make a tea and see if that's the flavor/smell. Actually that seems like a good idea for lots of hops. Then again that's the point of Smash recipes. Experimenting here I come. But I've strayed. See if it mellows over time and changes.
But if it is in-deed a sour taste/smell, buy new lines for next brew and clean everything real well. What do you use for sanitizing and How do you use it?