My 2012 520d had the guides and chain replaced at circa 35k miles.
Started in much the same way as jabroni80 has experienced - very faint ticking noise from the engine bay.
Took it into my local dealer who confirmed that there was an 'issue' with the guides and replaced them along with the chain.
Thankfully it was still under warranty so no nasty bills to cover, however it was in the dealership for the best part of a week. On the plus side they did give me a fully loaded F30 320d M-Sport whilst mine was being torn apart
