Black Noise

Is there such a thing as black noise?  I don't really know.  But I've heard of white noise and people say it really helps some kids sleep.  The other day we were having work done in our attic at the old house and it was super noisy--nails, saws, sanders, etc.  Isaiah walked around plugging his ears the whole time.  And then, although he hasn't napped in months, I found him in the living room sound asleep.  So whatever those super loud sounds were are apparently what he needs to lull him to sleep.