Sounds like subframe bushing to me. Just one thump? If you can repeat every time you start that particular way it's slack somewhere.

Tip up your rear seat and if necessary remove one of the plates over the gas tank and all the drive train and suspension sounds will be literally 10x as loud and much easier to tell what is going on: don't freak when you hear all the different slack work through the drivetrain when you shift gears from forward to reverse etc

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)