Off Flavor = Apple Skins?

All my kegged beer have a apple skin taste/aroma. It ranges from moderate to heavy and was present in my Kolsch, Haus Ale, and my most recent Oatmeal Stout.
I putting this in the kegging section because its only on the portion of the batches that I keg.
I've read/heard that that type of aroma/flavor can be related to the carbonic acid. None of these have been over carbed (as far as I know) they haven's been extra foamy or too bubbly for the particular style. Any suggestions?

The only thing i can think of is scrub the **** out of it and let it soak in star san for a day or two...and run the star san through the lines cuz that might be it