Vibration when stopped and in Drive?

[Agentlongwood]

My car is a 2014 MKS Ecoboost with about 61k miles on it.  When the car is up to temperature, and I have the A/C going and I'm stopped while in drive (or S) there is a constant humming type vibration that can be felt throughout the car.  It feels kind of like the idle is too low or something.  If I shift to neutral it goes away.  It also goes away as soon as the car starts moving again.  If I have the heat running and it's in the evening the vibration does not occur.  Mostly I want to know if this is normal or common or what.  To me it feels way too noticeable to be just normal operating vibration.  I just bought it recently, so I'm still getting used to what is normal on these cars. 

[SHOdded]

I would have said torque/engine/trans mounts first when you mentioned the vibration.  Belts/A/C compressor is another.

I don't think it is the PTU/RDU due to the fact that it goes away when the car is in motion.  The driveshaft tho, is a possibility, because it is disengaged in P and N, but engaged in all other modes.  If the vibration is in the floorboard, that is a good indicator.