I rev the engine and something thumps! Answered
So I got back from my drive today and came up the driveway in neutral just for funnzies, but while in neutral if I rev the engine up quickly, around 4k RPM's there is a serious thump. The whole car gives a pretty good shake when it happens. When I bring the RPM's up smoothly I don't notice it so I am not sure what it could be. I thought it may be a clutch engaging, but what would engage at that speed that wasn't in already. I also thought it might be a clutch disengaging, but that would result in a serious thump, just a smooth wined-down. The car is a 2003 dodge durango with 160,000 miles on it. It is an automatic which can somehow kill itself when trying to start going, and it is the coolest, most durable car ever.