skyline

Hi folks, my car totally pissed me off yesterday. When i hopped in my car, and start the engine, i hear this low pitch whistling kind of sound. Its especially noticable inside the car, but not too obvoius outside the car. As rpm goes up a little bit over 2k, the sound goes away, apparently the sound only occurs when idle or in P.

Could this be alternator problem ?
I brought my car in today, and i was told that its the alternator...

So they are replacing me an alternator. Is alternator the problem /