To hear an announcer in your dream indicates that you are being watched. Someone is watching your moves or are taking interest in your actions. Alternatively, hearing an announcer in your dream represents a voice from your subconscious.
If you dream that you hear an announcer at a sporting event, then it parallels the actions that you need to take in some area of your waking life.
To dream that you are an announcer means that you are busy observing things going around you instead of partaking in the action.