I had something that looked (as best as I can tell) exactly like that an my beer.
In my case, it was a dirty faucet. I had been using kleen-plugs but switched to the black faucet covers. When I cleaned the faucets and switched back to kleen-plugs, the problem went away.
Our situations are different, though. I think it had something to do with the yeast, and possibly the lack of cleanliness or exposure to air.
Sent from my iPhone using the sweet Home Brew app, cuz I'm a douche and I need everyone to know that I have an iPhone as if everyone else in the world doesn't have one.