The Median Sib

I was sleeping soundly awhile ago and through the fog of sleep I became aware of a sound.  Very rhythmic.  THUD! pause. . . THUD! pause . . . THUD! pause . . . THUD!  This went on and on.  Was it coming from my house?  What on earth was it?  I determined it was coming from outside - but very close.  I got up and looked out the front window.  Across the street, workers are building a new set of townhouses.  A large truck with bricks is parked there.  One guy is standing on the truck lifting a handful of bricks.  Another guy is standing on the ground.  First guy tosses the bricks to the second guy.  Second guy tosses the bricks into a stack next to the townhouse - THUD!  He turns to accept another handful of bricks and then tosses that handful into the stack - THUD!  Mystery solved.  Sleep ended.