Re: Lifter noise
listen to the mechanical fuel pump if your engine has that tipe, i was trouble with those tapping noise recently, it turn out to be my fuel pump was knocking, liste carefully use a piece of hose or a stethscope to your ears.
Not sure if they use that type of mechanical fuel pump yet that was an
outstanding suggestion/idea. Couldn't tell you how many mechs would tear into replacing lifters just to eventually figure out the fuel pump was bad.
Explanation, many GM engines used the front engine mounted mechanical fuel pump. It was driven via a cam off the actual camshaft via a metal rod. When the fuel pump actuator arm/diaphragm spring would weaken it would cause the rod to tap on the cam lobe just like a bad lifter.
However,
llerrad mentioned a strange "popping exhaust note". This would lead me to believe something is very likely amiss with the valve-train (but one never knows...). Could be a bad lifter that is bleeding down at higher rpm. Could also just be a rocker arm nut that backed off. Could be worse
I would suggest attempting to locate which side of the engine the ticking is on. If you have quad exhaust this could be as easy as listening to the popping you describe - or listen for the tick via stethoscope or long metal rod/extension to the ear method.
Once you determine the side, pull that valve cover and feel all of the rocker arms and push-rods as well as look for anything not matching the others etc.. You will most likely want to tap/rotate the engine over with the valve cover off to feel each rocker/push rod with-once the valves are closed. This way you may determine which is looser than the others. Best way would be to run the engine with the cover off but this involves creative oil control or clips for the rockers etc..
Lastly - did you happen to over rev the engine recently??
Good luck
