Right now I am in a rental as the dealer is looking at it.

2007 Maxima, 56K miles, oil changed religiously with Mobil-1 10W30 and Nissan Filter.

About a month ago, this started. When engine is started hot, after sitting for 20 minutes

On startup:

Oil light flashes about two seconds just as key is released
Sound like a real bad rod knock at the same time.

If I then turn off the engine, it will sometimes repeat the sound/light flash, sometimes not.

Engine runs fine otherwise, uses no oil.

On cold startup, there's a little rasp noise, but no oil pressure light flicker.

Oil level is good, and it's done this with two different Nissan oil filters installed.

Also, engine has a 'turbo whine' sound under load at above 4500 rpm or so. I have tried driving with serpentine belt off to rule out AC or Alternator. My guess is either power steering pump, the CVT or something in the engine (like timing chain guide issue that was a TSB).

Perhaps the startup knock and whine are related? Like if the timing chain tensioner is having a really bad day and leaking oil pressure on startup?

I would have to do the secondary guide and tensionors an see how the oil pump pick up looks and look at back cover to make sure the oil gallery gasket is not blown out. Is there a check engine light on?

No check engine light. Engine runs perfectly.

I just had a long talk with the dealer tech, and he still cannot replicate it. He is driving it some more to see if the timing chain guides could be an issue, and agreed that doing an oil analysis for bearing wear might not be a bad idea.