How loud is the whistle at idle? Does it seems to fluctuate somewhat with rpms, with the sound getting slightly louder and slightly higher pitched as rpms increase? Do you get the sound right away when you start, or does it take some time before you can hear it?
I think you and I have the exact same whistle. I don't know about full throttle, but I have all of the other symptoms. When I had it at the dealer to replace the idler pulley I had the mechanic listen to the sound. He was almost positive that its a vacuum leak, and he said that there wasn't much he could do to find it until it threw up a CEL. I asked if it would cause any problems, and he replied that its not really an issue unless it gets bad enough to cause a CEL. He said that to find the leak, he could try spraying carb cleaner at various points which would cause the engine to rev higher if the flammable liquid gets into the intake system through the leak and ignites with the fuel.
It takes about 15 minutes of driving around before I can hear it, presumably because the break, wherever it is, doesn't open up until the engine gets warm. I have to admit, it gets very loud and very annoying, but I can't afford what it might cost in labor to have someone tear apart the engine to find it.
