c-dub

My girls 08 yaris has been making a racket from under the hood and Sounds like a knocking coming from the passenger side where the accessories are. Its stays constant at idle and when you raise the rpms. I Pulled the accessory belt off and the noise went away. Put it back on and it was back. Pulled out a stethoscope and tried to listen for anything out of the ordinary on the a/c, alt and water pump. Think I can hear the noise coming from the water pump. Every thing else sounded normal, but I can hear the rattle when I put the scope on the water pump near the pulley just not as loud. Any ideas? Will a water pump make that big of a racket?