I can't hum a tune in my head, but I can "feel" a tune in my head. That's how I experience music in my head. I know that's different from hearing in my head because of the experiences I mentioned in one of my previous posts. That's why I can learn fairly simple music by ear. But this way of experiencing music in my head is very blurry and not very detailed, and that's why I need sheet music for longer and/or more complicated pieces.

I think what I am experiencing is more of an internal spatial thing. In my head, I am aware of musical intervals as being relationships between objects in space. Notes have a relationship to each other in space inside my head, but I don't hear them. Try to imagine if, in your brain, you think in terms of notes being objects, and some of them being on top of, or underneath of other ones in space. Then try to imagine that you don't see these objects, you just feel them. That's more the way I experience it. And for me, Rythm is just patterns that these objects form in time.