OK, we've ruled out chlorine, and Scottish yeast like 1728 or similar are pretty clean fermented cool (I don't get the 'smoky' character the yeast companies claim fermented @ 58F and I remember you saying you go cool with it), so I don't see phenols coming from there. But it could come from an infection - wild yeast or bacterial. Sparging too hot with bad pH can give you an unpleasant astringency, but not what I'd call phenols. I'd bet on infection - I run Beer Line Cleaner through my draft lines once or twice a year - it works. And if you have a cobra tap you could fill a glass through it - if it's good and clean from the cobra, you'll know it's the beer line. If not, infection came from the fermentor or keg. Just a thought.