I find it interesting how operators find this wrong. I think all audits should be unannounced. I have personally be in plants that I have witnessed them clean, reorganize, retrain their staff, and implement procedures that are NOT implemented on a daily basis just so they can pass an audit.
I do not find that industry 3rd party food safety audits provide any added assurances to the food safety of the final product on a day to day basis when they are scheduled ahead of time, because they do not provide a true snap shot of your company and how effectively its food safety system is managed.
If you don't have the confidence that you could successfully pass an unannounced audit then you have no confidence in your system at all. And your company's "food safety culture" is just a mask you wear when told to.