If I understand correctly, you are experiencing overcarbonation along with a sour aftertaste. If you stir the CO2 out of solution, the aftertaste disappears. Otherwise, everything tastes normal, is consistent within each batch, and there is so sign of infection.
If this is the case, you are probably tasting the carbonic bite of excessive CO2 - a sort of harsh, slightly sour taste that doesn't linger on the palate. The solution is fairly simple: Use less priming sugar. Your beer may simply be cooler than what Palmer assumes and thus have more CO2 dissolved in it before priming.
Cut back your priming sugar by 15-20% and see what happens.
The Fiesty(sic) Goat Brewery est. 2007 & Clusterfuggle Experimental Ales est. 2009
Planned: Fat Man Porter, sLambic II, Brettennial Falcon IPA, Flanders Red, Orange Blossom Mead
Primary: Winexpert Riesling Ice Wine, sLambic I
Secondary: Flanders Red
Kegged:Black or Blue EyePA, Cherrywood-aged Crystal Stout,
2013 dump volume: ~2 gallons