The auto idle stop feature requires a special battery ( AGM ) and the battery is enclosed in an actively ventilated ( fan cooled ) enclosure to prevent overheating if the engine is stopping and starting frequently.
The intake air duct for the battery enclosure terminates at an opening behind the grill. Most likely, that's what you are seeing.
Interesting. The first time I noticed it I was about to go to the dealer to get it fixed. I started looking at other pictures and noticed the same hole. Thanks for the info.
