Also... Having some answers to these additional questions will help with the diagnosis:
(1) Are you the original Owner of the vehicle? If not… what was the approximate mileage when you made the purchase?
(2) Historically… Do you choose Synthetic Motor Oil over Organics and what brands have you been using? (Mobil1, Syntec, Amsoil?) Type (Synthetic vs. Organic) & Viscosity (5W30?)
(3) Do you ever choose the Best Quality Oil Filters over the FRAM? (K&N, Mobil1 or Amsoil)
(4) Can you be more precise in describing the actual sounds and their locations around the engine compartment? Having somebody perform a “Cold Start to Low Idle” while you are standing in front of the engine compartment and listening will help you to be more precise.
Recently, another GMT Nation member with the same High Mileage GM 5.3L engine was complaining about a horrendous racket in his valve train upon immediate “Cold Start” and during the discussion that ensued …. some very interesting answers and simple solutions came to the fore to deal with the serious problem of having clogged and blocked oil orifices in the Valve Lifters. The best part was that the solutions were possible without involving any dramatic requirement to tear the upper engine block apart to remedy the situation.
This video post ...and contributions from other GMT Nation Members might be be just what you need to know to intervene before your own High Mileage Engine makes great trouble as time goes on. Please make sure that you possess some fair to decent mechanical skills before attempting what the Video OP suggests (He is an EXCELLENT Mechanic)… because there will be some superficial disassembly of the COP (Coil On Plug) harnesses on both banks and the removal of the Valve Covers to provide the access you will need to solve the problem. This is one of those jobs that having an extra pair of hands can really help... and save you one Helluva Big Headache:
http://gmtnation.co/forums/threads/oil-pressure-drops-tapping-engine-under-load.14755/#post-480711