I have a 2003 Silverado with the 4.8. It ticks at warm idle. It's not coming from under the hood. It can only be heard from around wheel wells and under the truck. Holds 40 psi oil pressure at idle and 60 going down the road. If I rev the engine, it goes away...but ultimately returns after a few moments. Only happens at idle. No sounds under load. Check engine light stays on sometimes, sometimes it's off. What can the issue be? Is this normal or no? I've heard the Vortec motors are noisy. Has 164,xxx miles. Is not abused or driven hard. Oil changes every 3,000 miles. Thanks!

 

Check your exhaust manifolds for broken bolts that go into the cylinder head. Very common for those to break and make a lifter type clicking noise. If there are any broken bolts, gotta take care of those first.

 

Exhaust! Just thought of it. My wife's Jeep was making a rattle that she was real worried about. Took a while to track down, but there was a pinhole in the muffler. Made a noise at warm idle, when she started it in the morning to warm up and came back out to it. Possible you've got a little hole somewhere in the exhaust system.