1. If the dreamer is shouting to someone, it represents a desperate need to reach that person. If the "someone" is unknown to the dreamer, the dreamer needs to seek information from someone as yet unknown - as phoning up a librarian to find out if the library has a certain book.
2. If someone is shouting at the dreamer, if the dreamer knows that person, then he has been shutting out vital communications from that person. If the shouter is unknown to the dreamer, then there is information that the dreamer needs to seek out.