Since I had the car, i've had this issue - hard to explain but basically when slowing down from any speed, the final part just before it stops (lets say from 20mph-ish downwards) the car has a sensation that I can only describe as feeling as though there is a pendulum in car swinging back to front making the car feel as though as it jerks forwards, pulls back, jerks forward, pulls back etc until it stops.
Its a low frequency sensation - each 'forwards/backwards' type motion occurs probably every 1-2 seconds.
Another way to describe it would be to say it feels like you are sitting on a swing going back and forth. There is nothing felt in the steering wheel, its more in the seat (suggesting rear of car?), and its not left/right, its forwards backwards.
It also does it when accelerating from very low speeds and stops once you past 20mph-ish, which makes me rule out breaks.
I have a manual, and it does it when slowing down in gear (i.e. only push in clutch right before stop), it does it when clutch is pushed in before I even start slowing down, and it does it in neutral.
Its a manual 2005 320d on what I think is SE suspension. I have changed the following but this little issue has persisted since day 1 and has been the same regardless (not got better or worse):
gear box mounts
new wheels & tyres
new upper front control arms
new front drop links
new engine pulley
oil/filter/air filter change