How to diagnose lifter failure before it really goes south?

[DK91105]

2019 silverado, 5.3 L84, 81k miles.  Last few weeks I have been hearing a light tapping noise. I am well aware of the regular noises the engine makes and this is a new one. Ive been around engines all my life and Ive heard what excessive valve lash sounds like and this definitely sounds like it.  I put my mechanics stethoscope on and listened to the engine on both sides and the tapping sounds like its coming from the drivers side. The sound is roughly 1/2 engine speed and never goes away after engine is warmed up fully. At idle its not even audible but as soon as I pickup the RPM to 1500 it gets very noticeable and only gets louder with higher RPM. It does not feel like its down on power and no codes have been thrown.  I pulled both valve covers today looking for obvious problems. All rockers feel ok wiggling them around by hand and I cant find any excessive play in any of them. All springs and retainers are present and look to be in good condition. I eyeballed the push rods as best I could with a light and inspection mirror and I didn't see anything obviously bent  I also checked to make sure none of the rocker arm bolts were loose while it was apart.  The thing is the noise is not awful yet and hard to pickup on video but its definitely there. I want to address this before it becomes potentially catastrophic. I'm out of warranty and when I called the only GM dealership id let touch it they quoted me 6k to put the same junk lifters back in and that was if the cam was ok. I priced a whole set of parts to delete and tune out the DFM and while I can definitely swing it the labor is quite intensive and something Id rather not do unless it was absolutely necessary.  What else can I do to make sure It is lifter noise before I open it up?

Edited Friday at 12:16 AM by DK91105

[silveradosid]

the only way i know of is to use an oscilloscope and a pressure transducer, but most people wouldn't even know how to do it

[64BAwagon]

Given the history on these I personally would just go ahead and delete it and move on with your life. I think theres zero chance that noise isnt something bad and the sooner you do it the better chance you have of saving the rest of the motor.