I have a 97 A4, front wheel drive manual. In first and second gear, if you try by letting the clutch out quickly, the car will make a loud boom like sounding noise as you enter the gear but then is immediately gone as you take off. After the noise has sounded, there is zero shifting or acceleration performance related issues after that-drives perfectly and strong. Does not do it when downshifting into first or second gear, does not do it when in reverse. I'd let it go but it is loud and clearly not good. I have some thoughts but would like to hear yours first. Thanks

 

could be engine mount broken

 

I noticed the same thing today. A broken engine mount makes sense because I have noticed my engine seems to be vibrating a bit more recently. Are the mounts fairly easy to see?

 

It's your snub mount -- Its only about a $50.00 rubber part on the front of the engine, like a buper for forward movement -- but a worn one will give you that feeling/noise that the transmission is being "shocked" when the clutch is let out.