I had an extremely fussy colicky infant. I never thought that noises would help him sleep. But I noticed he would sleep if I was holding him and talking to someone. One day he was overtired and screaming because he could not sleep, and I turned on the vacuum. He went straight to sleep. It got me thinking about why that would be. Almost all adults would not welcome a vacuum on to fall alseep. We got a white noise generator after and it helped him out.