My ninety-year-old mother lives in a retirement community. She kept hearing noises at night that sounded like machinery, but they didn’t really believe her, because the noise would stop when they answered her complaint. At my suggestion, she bought a recorder and recorded the noise. She still doesn’t know what the noise is, but it mysteriously stopped immediately after she played the recording for them. It does come on during the day sometimes, but it no longer interferes with her sleep.
They didn’t believe she heard a noise.