Any ideas on why there's a ticking sound?

I have an 08 Silverado 1500. 4.8L, V8. I'm up to 183k miles.
For the past year and a half, it'll make a ticking noise, usually right after it's
done warming up. The ticking will last for anywhere between 2 minutes and
15, and it sounds like its coming from the driver's side of the engine-
somewhere towards the back, but I can't say for sure. It'll speed up with an
increase in RPM and slow down with a decrease. I can't find any real
correlation between ticking and the tuck except for one thing.  It ticks until it
stops and doesn't start up again at all until the truck has completely cooled
down and warmed back up.  
Any ideas on what it is? It'll make the sound when in park, drive, reverse-
you name it. I got top name brand high mileage oil and that did absolutely
nothing to help the ticking.
I use the highest octane gasoline and get the oil changed regularly.