Transmission surge
 

I have a 04 AT and when the car is going at slow speed <25kmh and downshifts by itself from 3rd to 2nd it sometimes gives a surge...It only does this when going at low speeds and doesnt do it when downshifting nor any other gears.

Any ideas what could cause this?

what do you mean by surge? is it a surge in acceleration or deceleration or does it sound as if a u-joint, trans mount or motor mount is making noise?

A surge in deceleration like it feels like someone hit the car