so i am getting a whining noise coming from my engine bay, passenger side by the belts, first i thought it may be the alternator so i replaced that, but no luck, same noise is still there. i read a few things on here, and someone said to turn the AC on and see if it goes away, so i tried that and it kind of went away... but not all the way, anyone have any ideas?

 

Take off the supercharger.

 

Take a bottle of water with a sprayer, like a windex bottle or something, and start spraying hoses and stuff on that side. There is probably a vacuum leak or something. If you hear the noise go away for a second find where the hole is and wrap some tape around it if you can. Otherwise buy a new hose.

 

AC compressor, idler pully, belts themselves.

 

I'm betting AC compressor...
http://forums.maxima.org/showthread.php?t=506182
there's some links to video files in there that show you what a noisy AC compressor sounds like with ac on/off. if your noise doesn't subside completely when you turn the AC on then your bearing could be worse than mine, or maybe your clutch is slipping.

but I'm betting you have compressor noise. bypass the compressor with a 37" belt as described in the link and see if the noise goes away completely.

 

the a/c compressor bearing could be bad causing it to squeel. like he said above.

 

also, you could take a piece of vacuum hose, like 1/8" or similar, while the engine is running hold one end in your ear and carefully touch the other end to suspected areas- like ac compressor, idler, ps pump, alt. listen for matching bearing noise.

 

this only works if you add a bit of soap. that way it will bubble where the hole is.

 

the water will make the sound go away for a second though. at the shop we use brake clean..

 

was the alternator you got a rebuilt or remanufactured one?

The Nissan dealership told me that the whining wouldnt go away until you replaced it with a new one.

 

I've got an air conditioning idler that's either loose or not bolted in correctly and it whines quiet a bit on start-up and when sitting at the lights apparently, though I can't hear it from the inside.

Either that or the AC pulley. I don't think the compressor would make a whine...

 

had the same thing. turned out to be the A/C compressor.