I couldn't be more happy to see this thread. I bought a 2014 Explorer Limited on February 28 2014 and I have been experiencing this and several other problems from day 1. Seeing that others have verified this is likely exhaust gases, and this car was purchased as a family car so my wife and I could safely travel with our children (they are 3 and 1), I would like a PM from a Ford Customer Service Representative so we can start deciding the best fix for this. I have had several other issues that the dealer has not provided reasonable responses to (MFT doesn't take input when < 60 degrees F and my $595 paint is coming off all plastic parts) so I am extremely disappointed in this experience.
A complaint for the exhaust issues has been filed with the NHTSA.