Is this bad boy the cause of my rattle?

[ndfrigi]

Familiar rattle on my water pump too.
But it can be one of the idle pulley also.
What I did is, I removed the firewall cover and then let the engine run and use a plastic hose (like a stethoscope) and use one end of the hose to place it closer to each part along the belt cycle and one end of the hose close to my ear. You will really hear which one is making the rough sound.