*Sound happens again*
Mom steps out into hall.
Mom (using authoritative voice) - What's going on?
Daughter - huh?
Mom - What's that noise?
Daughter - What noise?
*Son's room is mysteriously silent*
Son - It was me.
Mom - What were you doing?
Son - It's kind of hard to explain...
*Mom opens son's bedroom door with a flourish*
Mom - Try!
*Son, lying on bed, points to foot board of bed*
Son - I was standing up there, and just fell back down here.
Mom - That's a bad idea. Go to sleep.
Son - Yes ma'am.
*Mom goes back to bed and giggles with Dad*