I am finally finishing up my project and have to put center speaker in between the studs. On one of the studs I have an electrical outlet box - will the outlet create some kind of interferance with the center channel speaker?

Is anything plugged into the outlet? The larger the draw the more likely it will cause interference.

That said, I don't think you would have much (if any) at the speaker wire level. Most electrical interference is introduced at the RCA level. With improperly shielded cables.