2016 A3 Hi Pitched Flutter noise
 

Since the car was new (now has 21k after 20 months) after it has been idle for at least the good part of a day once start the car and then when putting in gear to either go in reverse or forward, you will hear a hi pitch flutter noise from around the fire wall for about 1 - 2 seconds then it disappears and you never hear it again unless the car sits for a long time. This noise is intermittent and does not happen all the time and it happens in all types of weather/temps so you can't isolate - had to dealer three times and they saw no codes or could not replicate the issue. I have no other problem with the car. Anyone have any ideas?

Wow that's tough to troubleshoot. There are tons of things that can make a noise like you describe (especially without actually hearing it myself).
Diverter valve, PCV system or maybe a belt/pulley?