clunking in steering wheel

i know this is a common problem in impalas, but what exactly causes this again?

my dads impala is still under warrenty, so it wolnt cost us anything to fix it :)

just a bad design in the ISS (intermediate steering shaft) they have an updated design to replace it with, but if its your first time, they may just try to take it apart and re-lube it, which it usually ends up coming back.