Why cant i hear when i stretch and yawn?

When I'm really tired I'll yawn and stretch my shoulders up to my ears. For as long as I can remember, my hearing fades out until I stop the yawn and drop my shoulders. I guess I'm curious because I am not coveringmy ears and I know the only part of my ear being affected is my eaustacian tube. Do any students know what is going on here? Its the same type of ungoogleable question as why I can feel air being pulled and pushed through two little holes in the roof of my mouth that I can't find in anatomy books.