I worked on this issue last night...
I first replaced the PCV with a brand new one. Whistling was still present.
Then, I went on to the alternator. As suggested, I unplugged the 4 prong wiring harness off the bottom of the alternator. Went for a drive...still whistling.
My last resort was to replace the alternator with my spare. When I removed the old one from the car it spun freely, but I still had my doubts so I continued with installing the "new" one. Got it installed, went for a drive and STILL whistling.
I wasn't sure what to do at this point. So, I left the engine running and put a dowel stick as close to each pulley as possible and listened to the other end of the dowel stick for a whistle-type noise. I got nothing out of any of the pulleys other than the normal buzzing sounds from the bearings moving.
The only thing I can figure is that this is a vacuum related leak or my gatorback belt.