2001 Mazda 626 loud clicking noise in idle

My Mazda 626 LX V6 makes a loud clicking noise when idling. It only does it when I start the engine. In park the clicking follows the speed of the engine, but if I drive it about 10 feet it stops clicking. It won't start clicking again, until I turn off the engine and turn it back on. It makes no noises when driving down the road. The check engine light does not come on either. It sounds like its coming from under the rear valve cover or under the exhaust manifold. The car still drives fine.