2009 Tahoe 5.3 with 150000 miles.
I do get a slight lifter tic when it's cold but goes away after it has been warmed up. I have been using synthetic oil only since 65000.
I have been thinking about doing an oil additive to give the engine a good cleaning, thinking sludge and other shit may have been built up with this engine's age and miles.
What do you all suggest? Sea Foam? Marvel? ???
As
@gooffeyguy said, can you confirm it's a lifter tick?
I'm not a fan of diluting engine oil. Modern quality synthetics have safe types and quantities of detergents that don't alter their weight or viscosity, which is an oil's primary protective factors. Before you assume your engine is sludged up, consider this: I bought mine at 146K miles. I'm positive that the previous owner maintained it well, but I'll never know what oil was used. After 49K miles of my ownership consisting of Pennzoil platinum every 5K miles, this is what my valve train looked like at 195,000 miles:
I never used any engine oil additives, flushes, etc. If your engine is sludged to the point it's affecting oil to the lifters, then the last thing you should do is introduce harsh chemicals to try to quickly break it off the internal surfaces and hope it all flushes down to the oil pan. That'll just put even more solids in your oil system, potentially clogging the tiny passages such as those in the lifters and/or wedging the tiny moving parts within the AFM lifters, which are more susceptible to to dirty oil than the regular lifters. What you wanna do is exactly what you've been doing for the majority of your engine's life- use good oil to slowly and safely dissolve any solids so they can be removed as intended during an oil change.
On the other hand, your engine could be spotless inside and all manifold bolts intact and you do, in fact, have a ticking lifter. I had such a case. My Tahoe is mostly a weekend toy so it sits a lot. Sitting lets more oil drain from the top end than with a car that's ran more often. I had a (or some) failing lifter(s) that would tick at startup. Most likely AFM lifters. This often occurred for just a second or two but, once or twice, it ticked for a few minutes. I made it a habit, before I started the engine after sitting for 1-3 weeks, to hold the pedal to the floor to keep it from starting and crank the engine for a total of 20 seconds in two 10-second intervals. This primed the oil system and the ticking at startup was vastly reduced or eliminated. Appreciating that I at least had a warning of lifter issues, I did this for a year or so as I collected parts for an AFM delete.
In short, verify the source of the noise and go from there. You might just need a $40 set of manifold bolts and $25 set of manifold gaskets.
a transmission service WITH an additional service of aftermarket CVT additives on her 2020 Civic at her last oil change because they said that she needed it ASAP and the car doesn't even have 40,000miles on it. Basically scared her into buying a goofy trans service and they didn't even change the filter. 
