I hadn't really thought too much about it until I read your post, mscbryk, but I have noticed it with Grayson Hall's voiceovers. Usually she's always worried or screaming "BAR-NUH-BAS" as Julia, but when she does the voiceovers her voice is much deeper, and less over-the-top dramatic. I'd suspect that upon closer examination we'd probably notice that for many of the actors who did voiceovers on the show--that their voiceover readings were in a deeper register of their voice than their regular character performances.