I didn't see this covered, but I apologize if I've missed something.

I've always been annoyed at the voice telling 3PO "Who are you" sounding so unlike a strom trooper. I mean, I do understand that the intention behind it was probably to not ruin the reveal for the audience that the Empire was already on Bespin. But the voice just sounds a bit silly, all gruff and weird. Besides, I don't think a normal storm trooper voice would be immidiately recognizeble, especially since they haven't been heard since ANH, so I don't se any harm in adding that.

Or, if keeping the reveal at all costs is a high priority, the voice could be changed to a normal person's voice, implying that the line is spoken by an imperial officer. I'd be happy so long as anything is done to it.