Alternator whine
 

Has anyone noticed a whine coming from the alternator? I am not talking about noise coming into the radio. When the alternator is not charging, and you are driving on a smooth road, you notice a whine between 2000 prm - 3000 rpm. The Nissan dealer changed the alternator at a cost of $800 to the extended warranty company, but the new alternator is just as noisy. They are checking with Nissan to ask if something else is causing the whine. As an old timer, I believe it is the alternator - new or not. When you reduce rpm, the whine decreases. If you have the AC off, and are sitting still, you can make the whine go up or down as the RPM changes. When the alternator is showing 14.4 (charging), the noise is not there.
If anyone has this problem or has had it corrected, please let me know.

Pretty sure you are talking about the ECU whine. It is a known issue that bothers some and not others. Depends on your hearing. Younger women have the best ears for hearing it. There was one guy who took it to a dealer, and they didn't want to acknowledge the problem until the young secretary rode along and noticed the whine immediately. The fix is replacing the ECU.

You need to figure out where the noise is coming from. If from the cabin, then JARblue is probably right about it being the ECM. If it's coming from under the hood, use a mechanic's stethoscope or a piece of hose to pinpoint (being VERY careful around moving parts).

Update
 

The alternator was replaced but the whine remained. I was told it was the idler pulley so they replaced that. Next, I was told it was the power steering pump so they replaced that. The noise is now gone, so it was the power steering pump even though the noise was not there if the alternator was charging but present if not charging.
So, after three "guesses", and a cost of $2700 to the extended warranty company, it is fixed. The vehicle is a 2012 with 34,500 miles.

How much was for the power steering pump replacement? I have had the same whine exactly as you described it for two years now. Took it in to two different Nissan dealers, one acknowledged the noise but refuse to warranty it and the second dealer (Fontana Nissan) said they can't hear anything and ran my car into a street light:cool:

Toss a diamond necklace under the hood. That'll stop whining every time.

Does the ECU whine has any adverse impact on the operation or durability of the ECU?

I had this whine too. They replaced the P/S reservoir, no more whine. There was a tsb for this on the infiniti side. I imagine there's one for the 370z too.

http://www.infinitig37.com/TSB/ITB12-035.pdf

Now it is possible your noise was indeed due to a bad p/s pump. Mine sounded like a supercharger whine. It was present mostly after the car was warmed up, especially in ambient temps over 60F. Just turning the wheel one way or the other while stationary would cause the whine.