I like Gould as a person (though not personally), so his humming and such I find somewhat humorous, and not bothersome at all. It's one of his trademarks. He does hum in practically every recording, and if you don't hear it in a particular piece, it's probably because it was edited out. Generally, I find that his interpretations, if not "acceptable" by normal standards, are at least interesting and fun to listen to. His Mozart Fantasie in d minor would be a good example of this, I think... has anyone here heard it, by chance? If you don't laugh at it, you'll loathe it. (I can upload it to my webspace if someone here asks.)
My teacher said that he played much of his Mozart like an ambitious toddler.

I'm not sure if I would go so far myself, but I did think that was funny.
But, regarding his humming, I do remember reading that when Glenn was very young, his mother (a piano teacher) would often play the piano in front of him, singing along with whatever piece she would be playing. So, chances are that when he himself started playing, he did the same from the start. It seems like this humming was ingrained into his actual piano playing technique from the start, so not to hum would be uncomfortable for him. I don't think he was doing it just to be annoying.

An interesting note is that when Glenn was just born, his parents said that, instead of crying as most babies do, he was humming.
If you haven't heard it yet, you can listen to him sing and play Strauss' Burleske for piano and orchestra at
https://www.collectionscanada.ca/glenngould/m23-700-e.html. It's... er, hm. Listen to it. (You can also find a bunch of other recording sessions there which you might like.)
P.S. Hm... my first post...
