I actually found out about this by accident. I followed a girl in her 135i convertible because I wanted to complement her on her 19" CSL rims. She said to me "Hear that ticking noise? Get it fixed. I got mine fixed. It's something to do with air in 'somewhere' and they need to bleed it out".
So, I went into my dealer and got it fixed. Easy.
///M135i: AUTO | ALPINE WHITE | CORAL RED LEATHER | HEATED SEATS | SUNROOF | NAV | DAB TUNER | HARMAN KARDON | PERFORMANCE BITS 'N' PIECES