1st post here but worth the concern. I just bout a 2016 200 limited 95000 miles and there is what sound like a heat shield rattle but only happens when the car is in drive and foot on the brake idling. When in motion sound goes away and when in neutral or park sound goes away. Is this mechanical or just engine movement. Its hard to pin down because I have to have it in drive to hear sound and its not all the time.
thanks

 

Sounds are almost impossible to diagnose meaningfully over the internet even with a recording. When it's by description, then I wouldn't trust any remote diagnosis. Your best bet would be to get it up on a hoist and get under there and listen to it, maybe with a mechanic's stethoscope to pinpoint the sound. Many years ago I had a sound like that in my Concorde which turned out to be a baffle in a catalytic converter. You could be right about a heat shield but somebody's going to have to get under there and get up close and personal with it to be sure.