I have a ticking in my 2004 Silverado 4x4 with the 5.3l vortec, aprox 167,000 miles. I had a check engine light on and replaced the intake manifold gasket along with a knock sensor and now the small tickI had has got worse, it almost sounds like it's from underneath, I don't believe it's lift or because I barely had a tick a month ago, if you have suggestions please let me know. Check out the video

 

Check for broken off bolts in your exhaust manifolds. If you have any broken ones, they're most likely on the back cylinders on each bank. Relatively easy fix, I always pick up bolts and new gaskets from the dealer. New design on the bolts, and the MLS style exhaust gaskets work really nice and are really heavy duty. I usually recommend you remove the exhaust manifolds, weld a nut to the remaining bolts that are still suck in the cylinder head, then turn them out with a wrench. Somewhat of an easy fix, but may not necessarily be easy to get the old broken bolts out of the cylinder heads.