Sorry I can't find my old thread but I'll be brief. Problem started out as a loud Chirping Noise then a slight ticking noise at Idle. I thought the noise was coming from the Flywheel/Torque Converter area. The Tranny has 427,000 original miles,so I took it to a tranny shop they dropped the tranny rebuilt it and replaced the TC and Flywheel. The Chirping is gone but there is an intermittent ticking noise at Idle Sounds like it's coming from under the upper Plenum when under the hood and when under the car sounds like the Flywheel area, Anyone have any idea what it might be? the truck runs smooth and the noise comes and goes Please Help

 

I don't how miles your engine has on it, it could could be a valve related problem like a hydralic lifter failing. 4.3L Vortecs are push rod engines, so your camshaft and lifters are in the middle of your engine which would explain why you can hear it from the top and the bottom of the engine.