Over at End the War on Freedom I found this interesting link to a piece by Carl F. Worden on Police Contact.
Mr. Worden advises absolute silence in any & all encounters with the police & I generally agree. However the one time you should not be silent is when an officer attempts to violate your Rights. In that instance one should briefly but concisely remind the officer that his actions would be a violation of your Rights & inform him you will use every legal means at your disposal to protect your Rights &/or seek restitution if they are violated. But in no way should you say anything that could incriminate you. Leave out any personal details & stick to the general idea.
Read what Mr. Worden has to say about silence. It may come in handy.