I think you need a banner of Brian with his mouth open and that little devil guy popping out of it! LOL
And even with his spoken voice, he sounds hoarse and unsure of himself, like people who can't hear what they are saying. I don't know, just my thinking. If I'm right, you all owe me a dollar! LOL
Mare, you could be wrong, but with the training you have, I'd say you're definitely onto something, whether it's the whole problem or not! Has anyone seen the video of the soundcheck in China where they're singing "In A World Like This" and Nick and Brian are doing their ad libs-- Nick is totally helping Brian find his notes with hand gestures. It's actually a really cute Frick and Frack moment, but I'd never really put two and two together. Nick is stooping down and pointing up with his finger while Brian watches as he sings. Brian nails it, by the way, but I think the hearing thing definitely makes sense. Now, here's where my professional training comes in, and it may be totally out in left field, but one of the primary drugs that is used to treat bacterial endocarditis is notorious for causing ototoxicity, which can manifest as hearing loss in later years.
I kind of just had an aha! moment there, Like Mare, I hope it's not the case, but it kind of makes sense.