For 60k miles the cause of and solution to the high RPM screeching noise has evaded me. Across the internet there have been countless theories about what causes it: airbox, serpentine belt, pulley, timing chain, exhaust, VVEL. The concensus is it is annoying but harmless. I have always believed it was an internal engine noise as I have noticed minor deviations when changing oils. Sometimes it would quiet or go away after an oil change but come back shortly thereafter. As I tend to use whatever premium synthetic is on sale, I have also noticed very slight differences with different brands.

On my last oil change at 92k mi, I filled with pennzoil ultra platinum (which I have used previously) and, knowing that nissan has prescribed oil with an ester additive to quiet other noises with the VVEL system, grabbed a 15oz bottle of Lubegard Biotech and dumped it in. After driving a couple hundred miles, I noticed the high rpm screech was gone. It has not come back in 4000 miles.

I would be interested to know if anyone else who has experienced the high rpm screech has seen it disappear with nissan ester oil or ester based oils like motul or redline.