I actually can't whistle, I lost my whistle after a newyears eve party a couple of years ago. Odd but true. Just couldn't whistle anymore.
I never hum either. I have a very clear and LOUD voice and instead of a pleasant quiet hum of a tune I have in my head I will sing it loudly. My husband says he loves it when I sing, They say love is blind, I think it must also be deaf. I can easily make our poor rat terriers howl.