Our next door neighbours were a bit older than us (the husband is now deceased) and we were surprised when we started to hear loud, rhythmic creaking through the wall. It was always in the morning, usually when we were getting up. The husband was recently retired and we thought they must be making the most of their extra time together! My husband was particularly impressed by his stamina, as it was so frequent and went on for so long.
Our DD was great friends with their son, having grown up together. When he came home on a visit, they went out for a drink and DD let slip that we could hear his mum and dad. The son could not stop laughing. Turned out that it wasn't their creaking bed, it was his mum exercising on her rebounder.
Unfortunately, when they got back home, the son said to his mum, "Do you know what next door thought you were doing in the morning?" The poor woman was mortified. We never heard it again.