There are dozens of threads on this already. You will get very adament responses that yes you should tell, and equally adament responses that no you should not. Just like open carry v. concealed carry.
So let's try to summaraize the responses:
1. Follow the law. If the law requires you to notify, then you notify. Otherwise:
2. Your lawfully carried firearm has absolutely nothing to do with the traffic stop. To avoid any potential hassle, keep your mouth shut about it.
3. If the cop sees the gun accidentally or is otherwise surprised by it, they will potentially take forceful action against you, so tell them up front to avoid that.
4. If you show your permit and tell them up front about your gun, you are giving them legal justification to seize your gun, frisk you, and perform a search of the vehicle from which you may immediately obtain another weapon, all without your consent, until they can verify the validity of your permit, so just keep your mouth shut to avoid that.
5. They might know you have a permit anyway, once they run your name and birthdate/address from your driver's license, so just tell them up front.
6. If you don't tell them up front, and they find out about your permit from the dispatcher, they might wonder why you didn't tell them and treat you badly for it, so tell them up front to avoid that.
7. Once they find out about your permit from dispatcher, they now know that you have passed a background check and any weapon you might have is 99% chance completely legal, so they shouldn't bother you at all once they find out you have a VALID permit, so don't tell them. If you do tell them first, they have no way of knowing if your permit is valid or not (see #4 above).
8. They just want to go home safe to their family at the end of their shift. I have no idea what this has to do with telling them about your gun, but some poeple claim that is a reason to inform them.
9. It's polite. Again, I don't see how telling them about the gun and permit is polite, but some people claim it is. So should you also be polite to bus driver's, taxi driver's and convenience store clerks and tell them about your gun and permit too at first opportunity?
10. I want to go home safe to my family at night without being hassled by a police officer about my gun, so I won't tell them because that only invites hassle (whether or not the officer hassles me is up to them, but I don't need to give them a reason to.)
11. The safest place for my gun is in it's holster not being touched by anyone. Telling the officer about the gun invites them to disarm you, causing needless handling of the gun, placing everyone in added danger from a negligent discharge.
12. You should tell them about your permit because it will prove to the officer that you are a good guy and maybe they will be more inclined to let you out of a ticket. (Not the reason I got my permit, but some people use it for that.)
13. My 4th Amendment rights are just as important to me as the others are, so I won't tell them about my gun and invite them to take it from me.
14. If you have nothing to hide, why not tell them about it?
15. Just because I have nothing to hide is no reason to tell them about any object I lawfully possess, including my firearm.
16. If they want to know if I have a gun, why not just ask me? If they aren't concerned enough to ask, I am not concerned enough to offer.
I am sure I will think of more responses and others will add their own.