I think internal noise is the most distracting for me personally. When I am listening to a message or a lesson of some kind I struggle to maintain focus on what I am hearing. I tend to be distracted by my own thoughts to the point where I completely tune out what I am supposed to be listening to. One of the main ways I keep myself on track is repeating every word that the speaker says in my own head. It helps give me something specific to think about, while also keeping me engaged and processing what the speaker has to say.
Internal noise gets me too! But repeating every word that the speaker says in your head is SUCH a good idea! I'll have to try that sometime :)