Water pump received with a rattle

A diagnostic scanner shows the main water pump on my wife's 2010 Prius went bad (code P261B). I ordered a new AISIN WPT-190 replacement pump online. When the new pump arrived, it was poorly packaged and the box was a little beat up looking. The pump looks ok out-of-the-box, and the impeller spins freely, but I notice it has a rattle sound. The rattle does not sound like a piece that's completely loose and flying around freely inside the pump housing. Rather, it sounds like a metal piece sliding back and forth along the impeller shaft. I suppose that sound could be normal, but I need to know for sure before I install it. What do you think?

 

Right after posting my question, I found the answer, although I'm a little embarrassed... The noise is coming from a metal washer at the end of the impeller shaft that is allowed to slide back and forth about a quarter inch or so.