I've got a constant, though fairly quiet, chain noise. A friend who doesn't ride fixed commented on it recently and I had never thought twice about it. He said it could be possible that the rear sprocket wasn't in line with the front, or something to that effect.

What's normal? Should I be worried? The rear wheel is straight, chain tension is good. There's nothing obviously wrong with it in my eyes.

It's a 2002 Bianchi Pista, by the way. Two months old.