In Star Trek IV: The Voyage Home, the survival of Earth depends on a mysterious probe having a conversation with humpback whales.
McCOY: Well, dammit? You think this is its way of saying 'Hi there' to the people of the Earth?
SPOCK: There are other forms on intelligence on Earth, Doctor. Only human arrogance would assume the message must be meant for man....
What was the message?
This isn't answered in the film itself, and the topic is never revisited in Star Trek episodes or other films. But perhaps there are screenplay notes, novels, or comics that elaborate on the probe's message.
I do not believe that the conversation is an exchange of random sounds without meaning, given this:
KIRK: Spock, could the humpback's answer to this call be simulated?
SPOCK: The sounds, but not the language. We would be responding in gibberish.
In other words, the premise of the film relies on the assumption that something specific was being communicated.
As best as I can tell, Memory Alpha and Memory Beta's entries on the probe have no information regarding this particular question.