I hit on this thread while whistling along with some of Gillian Welch's songs that have that Appalachian backwoods sound (I compiled my own CD of selections off of her published albums). Whistling is something I do frequently when I'm alone or listening to whistle-able music.
I once had a older neighbor who was an old-time guitar and mandolin player. (I loved 'jamming' with him; me on guitar, him on mandolin.) When he would be out mowing his lawn, he'd be whisling so loud he could be heard above the sound of the mower all the way over at my house which was some distance away. He was a highly practiced whistler though; he could bend notes and get a distinct simultaneous multi-note sound just by the way he held his lips. I've never been able to do that.
SC