I have an audio recording of this happening. It went on for over a mile, stopped then came back again. This is about the fourth time it's happened while I've driven it. Probably the sixth or seventh for my wife. Dealer keeps saying they don't have a code so they can't find anything. Well it sounds like an air hammer being used on the frame when your inside the vehicle. The vehicle physically shakes from the impact of whatever is slamming together. The source is literally right below and forward a bit from the shifter. I'm stuck driving this POS Fiat now since my wife is afraid of it. and if the dealer doesn't fix this crap, I'll drive it until it blows up and leave it on their lot for the public to see. Garbage, I'll never buy another Jeep/Chrysler anything unless it's pre-Fiat.