I registered on this forum just now after finding this thread. My 2014 3.7 suffers from this same issue. I purchased it on April 2nd, 2013 and currently have 6,400 miles on it. The vibration has been happening occasionally since ~1,500 miles or so. I can now almost always reproduce it on command. Typically occurs when lifting somewhere in the 2-3k RPM range, but can also happen higher up in the rev band. It was very disconcerting at first, as I thought perhaps I had done some type of damage. I am, IMO, easy on the car. Rarely above 5.5k, never above 6.5k, no hard shifting or crazy hooning. It is my DD. I'm not sure if I need to take it to the dealer or if it just a byproduct of the design?
I also have a rattle that occurs in 2nd, 3rd and 4th under very light acceleration that sounds like something is loose around the firewall. I have visually inspected and found nothing. I installed the Roush axle-backs around 3,800k which mitigated the noise somewhat under most conditions. Should I take the car back to the dealer (about 1 hour away) or see if the issues worsen over time?
Airaid CAI, Roush axle-backs, Roush high flow upper grill, Raxiom Smoked Projector HIDs