I can't put my finger on it, but the vast majority of my lighter brews (PAs, IPAs, etc) all have this underlying similar flavor. Thats not to say they all taste the same, but there is something very similar in their smell and, umm, the after-burping taste.
I've changed everything trying to isolate it. Changed sanitizers, built a better mash-tun, switched up recipes thinking it was a common grain, etc. Could bottle conditioning just create a common flavor? I keep considering switching to kegging, but I like being able to hand out mix and match six-packs to friends/family; plus, my little condo doesn't have much room for a keggerator.
I wish I could describe the flavor... My palate is not great, so I hesitate to say acetaldehyde because it doesn't exactly taste like green-apples to me, and I notice it in beers that have been conditioned for months.