We moved into a student rental house (many years ago), which always had a background noise of running water. We always assumed it was because there was a newer housing estate built beyond the house, and we were hearing the water main supplying that estate. Then one night, the Water Board appeared outside with diggers, and asked if we had noticed any subsidence, as somebody a few houses away had water in his basement. It turned out that there had been a leak in the water main outside the property for several years, which had gradually eroded away the grass verge in front of the house, from underneath. Once it was fixed, we couldn't get used to the silence, it was like waiting for the other shoe to drop.