Clicking sound in engine

What is your question?

Off and on for the past 2 1/2 years, my 2006 Hyundai Elantra has made a "clicking" sound. The noise sounds like a cross between the "ticking" sound when the oil is low and the "clicking" sound of the Wheel of Fortune wheel when spinning. Its very loud. The more the engine is revved, the louder it gets. But when the RPMs reach 1000, the noise stops. Like I said, the noise comes and goes. Any ideas of what would make cause this noise? Changing the oil doesn't help. And, the oil level doesn't seem to be a factor