The milk float and the chink of the bottles placed on steps in the very early hours of the morning, when you knew you could turn over and have another sleep.
Actually, we do still have a milkman who comes down our road to visit a couple of houses. Until fairly recently he did use an electric float and I would occasionally hear it at about 3am, and it would take me right back to my childhood. Unfortunately he now uses a 4x4 which doesn't have the same effect!