I both a used 2012 Lincoln MKX at Findlay Audi dealership in Hendersont December 2017. I found out my tires were manufactured 2011 and creating loud humming noise and afraid the safety . Any suggestion ?

Take the car back to the dealership and see if they're willing to change the tires. Maybe have the tires independently inspected by a reputable tire retailer first. When you visually indirect the tires, are there noticable cracks in the sidewalls? I don't believe the dealer is liable to replace the tires in this situation, but they may be willing to do so to maintain a customer service reputation. "The squeaky wheel gets the grease," as they say. If they refuse, and the tires are actually bad, take it to social media. They may consider the cost of a new set of tires more valuable than bad reviews on popular sites, but i don't think they're legally obligated. It's your responsibility as the buyer to inspect those sorts of things when buying a 6+ year old car. Ford does recommend changing tires after 6 years, but it's not a legal requirement. But, most reportable dealers will replace worn tires before selling a used vehicle.

I do not think the sound that your tires make will affect your vehicle passing the safety inspection.