I've had the same issue, Had a fresh keg on and thought.. hmm this tastes a little weird.. pulled down the taps and saw the same thing.. funny how your beer tastes alot better once you don't have a old hops and beer strainer..
I flush my taps too at each keg change. I need to actually take the taps apart to clean this out. I did notice a slower flow rate, thought the flow control was playing up!