Accelerating from a stop the engine makes a horrible knocking sound and will barely move (even with more throttle). When I first got the car I noticed this but had assumed the sound and harsh vibrations were simply caused by wheel hop. Mainly, because the sound would only be made under hard acceleration from a stop (when you are turning left into fast traffic from a stop sign). However, it started to be more common as months went on. I didn't hear tire squeal or loss of traction so wheel hop didn't really make sense. If it is wheel hop, the heavy car is strangely prone to it.