Engine Thumping while idling -1997 Buick Century?

[shanmotley]

I have a 1997 Buick century that has started to make a slight engine thumping noise - right side of the car. It only makes the noise when idling - not while driving. Any ideas what it might be?

 

[Ronnie Wrench]

Harmonic balancer.Common problem on a v-6 buick.Its the big pulley on the bottom.remove belt it should rock back and forth if bad