There is something definitely not completey right with your Venture. Yes all Ventures "Chug" when they idle, but not that they rattle things. I have accidentally pulled away from a light in 3rd gear a couple of times and the bike complains abit, but does not rattle the dash. I've been known ( I know its not right) to cruise thru small towns two up with the tent trailer behind in 5th gear @ 25 - 30 Mph and it will pull cleanly back to 60 mph ( notice I did not say briskly). Sounds like one cylinder is not running right, when the Black box calved on my 85, the thing first started to miss slightly on one cylinder til around 3000 RPM, then it went away, then the cylinder just went dead, then another cylinder started the same thing - then we had a Harley ( chugged on 2 cylinders ) and then it died. Got a new Black Box and everything was all better! Turned out the stealer had filled the Battery with it in the bike and Acid had spilled and after time had eaten the connectors on the Black box and also some of the metal in the area that it had come in contact with. We all thought it was the Box that had corroded contacts but could not explain the other metal damage. A little bird informed us that a Pre-delivery /tech had been fired for half heartedly servicing brand new bikes and that more than one had come back with problems!