When you are doing something that makes sound and you don't want other people to know you are doing that activity. So you try to cover up the noise you make with another thing that makes noise.
When you poop you turn the bathroom fan on to create a sound barrier.
When you masturbate and other people are in the house you turn the T.V. louder.
A fictional object used as a hazingjoke pulled on unsuspecting newcomers in the U.S. Navy.
Corporal Dodson: Colonel, the phone died.
Colonel Watts: Go down to the Supply deck to see if there are any sound-powered phone batteries.
Corporal: Sir, yes sir!
Watts: *chuckles*