My '99 A6 2.4V6 quattro (5-spd MT) avant is giving my serious headaches.

It rocks back/forth like a temperamental horse when driving in slow traffic, lightly on/off the throttle. Its beyond annoying, people get queezy after a while. Otherwise, when driving, unless I disengage the clutch slowly and smooth as baby-virgin-kitten-silk - I get a nasty *thud* inside the cabin. A friend couldn't recognize the noise from the outside. I'm really worried about the impact it could have on gearbox and rear differential though, so I'm hoping to get it sorted sooner rather than later.

I've been suspecting engine mounts / tranny mount / rear diff mounts, but I really don't know what I'm looking for, or how much/what nature of movement is normal. Diagnosing worn rubber and joints is really not my strong suits. I can't afford to just blindly throw parts at it, hoping that one might stick.

So I made a short 1-min video clip when trying to take off in 1st and reverse, with parking brake engaged. I have a slightly sticky rear caliper so I wasn't able to give it the full boot and staying in same place, but it should hopefully be enough to determine; If the engine is moving excessively? And hopefully, any indication of what might be the culprit?

-Videoclip-