Cold air is rushing in from the passenger side footboard. How to stop it ?

What is your question?

Cold air is rushing in, even when the heater is running, from the passenger side footboard. This gets bad when driving above 50 miles/hour. In a recent trip to Minnesota, the passenger side was getting cold due to air rushing in. This happened after the hyundai dealers put in the Hyundai warranted guards (which was done right before the trip). I took the car to the dealer who worked on my car, and they are saying there is no problem. But there is definitely some thing wrong. I have been driving this car since 2006 and I drove it in harsh cold winters of Minnesota and Pensylvannia, but everything was fine before they installed the guards. I want to know if while putting in the guards could they accidentally left an opening or what else could led to such a problem. I am at a loss. So if I get an idea what may be causing it, I could talk to the repair guys better. Thanks