Do the sides reveal their goals when the haunt begins?
When the haunt starts the new rules are only known by the side that they are for and not everyone.

The traitor generally leaves the room to read the rules that apply to them and it will give them some idea of what they need to do to win and what their former friends are going to do. At the same time the rest of the group will read their rules and it will give them some idea of what they need to do to win and what the traitor is doing.

The only time this changes is when a haunt lets a traitor convert other players then that player will also get to read the traitor rules and they will now know both sets of rules.