Why do whirring noises put me to sleep?

whirring noise example: hoover, car on motorway, fan, humming from an air con, spin cycle on a washing machine. They make stop what im doing and make me very sleeps, so sleepy the noise canceles out the suddenly comes back when i tryto concentrate. Sometimes washing machines on spin cycle make me stand and stare into space. Its always hapened when im alone or when its quiet so i have nothing else holding my attention