1998 Honda Accord - Strange Whine

I drive a 1998 Honda Accord V6 4Dr 3.0 - 95000 miles.
When I start the car, I hear a high pitched whining noise, which continues for as long as the car is idling. When the car revs or is moving at high speeds, the sound is absent, at least to my hearing. The noise spikes to its highest pitch/volume on startup, and settles to a slow steady whine while idling.
It appears to increase slightly in pitch/volume as more load is put on the engine (such as using the A/C).
It appeared to be coming from my Serpentine Belt driving the A/C and alternator, so I replaced this, but I am still hearing it. Any ideas on what this might be?

*Edit* This noise is much easier to hear from inside the cabin of the car than when standing in front with the hood open