I just recently started getting an underhood whine when I rev my motor or even drive down the road. I don't hear it at idle but under any load I can hear it. It almost sounds like a quiet blower whine. I noticed today that my voltage meter dropped lower than it normally does when I was sitting at a red light. I thought the whine could have been from the A/C compressor but I'm not so sure now. I am almost positive it's not the waterpump because I replaced it a little over a year ago.

So does it sound like the alternator is "on its way out"?

 

It could just be your belt. TO test the alternator you can rip it out and bring it to autozone to get tested (PITA), or turn the car on and bring up a constant rev nd see if your volts go up. If it is recharging the battery and volts go up, your alt is probably good.