The mighty vortec tic!
It used to drive me nuts. I don't even notice it anymore,
If it comes and goes. Louder some days?! Try looking at the Pcv valve, if it does it all the time do an oil flush with ATF then run Lucas valvoline 5-30
(I'm not a fan of synthetics in trucks!! They free up power but are noisy) also look at your climate? It's about 105 in the summer where I live so I run a little Heavy and lighter weight in the winter. Plus I'm always pulling a boat.