Even though you do the humming in a dream it doesn’t count as a Realilty Check. You aren’t testing reality, you’re testing your ability to hum. Even good solid reality checks can trip you up. I’ve seen people stab themselves with a pin in a dream, not feel any pain, and still not become lucid.

I personally never do RCs awake or asleep. I become lucid occasionally thru Dream Signs, but most commonly by spontaneously realizing that I am dreaming. Reality Checks can become a crutch; a rubber crutch that will let you down from time to time. They have been enormously useful to may people, but they have also proved to be an enormous pain to many others. Test the waters.