At last, the mystery is solved. For 20 years I’ve wondered what it was, that noise we often hear in the garden. Sometimes it sounds like a duckling quacking, as it takes its first swim. At other times, it resembles the plaintive bleeps a baby crocodile makes, moments before hatching. I’ve even asked our neighbour if her terrier has a squeaky dog toy. Then, in the recent spell of Bank Holiday heat, the secret musician finally revealed itself.