Another thought. Think of a subject you can randomly talk about for two or three minutes, or ask your brother to talk with you for perhaps slightly longer than that and record it. Wait at least another 10 minutes or so before playing it back so you'll be objective. See if you can pick up some of this "flatness" or irregularities on your own. Keep in mind that your voice will sound differently than what you're used to and that's normal, but can you pick up anything else? If you can and you believe it's a concern, it may be time to broach the parents about it.