Never happened to me
Are you sure you did not leave the car on by mistake when you first got out? Embarrassingly, I have done this by mistake more then once, but each time I had the fob on me and the horn beeps reminded me that the car was still on. I know what you wrote, but is it possible that the car was left on.
. Could it be the hot engine metal parts starting to cool down? If not, here's an interesting one - the C has a sound cancellation feature whereby mostly inaudible noise is purposely fed out of the speakers to help cancel out the outside noise. Don't ask me how it works...one of the forums techies can fill you in. However, on a few occasions I have entered my garage, turn everything off, go into the house - and then a few minutes later opened the rear hatch to either put something in or get something out and I can hear the noise cancellation coming out of the hatch speakers for a few minutes even though the car has been off for at least 5 minutes. It eventually stops.
Now most of my comments probably have been little help to you, but in the 6 months and 6k miles in which I've had my car I've experienced at least 6-10...what I call "glitches" that seem to come and go...most of which never return again. For a premium car these "glitches" are very annoying, but by the time I make my list of things that need to be fixed, I find myself crossing off items because these "glitches " have mostly disappeared. I've never had this happen to me in a new vehicle before and it is a reason why I am not completely satisfied with this car. However, after reading about other peoples experiences, I'm lucky that my "glitches" have mostly gone away leaving me with a short and not terribly troublesome list for my dealer to fix. As this forum has brought to light, the C is a very inconsistent car. The quality control in Louisville must leave something to be desired.
After 2 trips to the dealer in 6 months the only item they have not been able to fix is the cooled/heated front seat backs
that do not work. The seat bottoms cool/heat fine, but not the backs. Trip #3
to the dealer to fix it occurs in a couple weeks and they claim that they've done the entire TSB and the car just doesn't push enough air to the seat backs. They will take the seat apart again because after my call to Lincoln, they told the dealer to do the TSB again. I'm not holding my breath for a better result..