Milburn's accent

I'm surprised that I have yet to see this nitpick. Was anyone else just a little bugged by Rafe Spall's inconsistent American accent? When we first meet him, he has a southern accent. It's okay, there's nothing really wrong with it, but to me it does sound a little unnatural. For almost all of his other scenes, he speaks with a nuetral American accent, which to me sounds more authentic. Right before the introduction of the hammerpedes, his southern accent briefly returns.

Anyone else annoyed by this? I know it's really unimportant. Do non-American fans even notice this?