I donated by the open surgery, so there was no gas. But there WAS lots of bubbling and gurgling. When the kidney is removed, all the neighboring organs have to shift around until they find comfortable positions and fill in the gap left by the removed kidney. Meanwhile the body fills the spaces with fluids for protection. Takes a while for everything to settle into new locations. (In case you haven't guessed, this is not a highly scientific description.) I found that bending and stretching exercsies were very helpful. Especailly good was just stretching out on my back on the floor with arms and legs stretched out, then moving onto each side for a while. Felt like a water cooler was bubbling inside me, if not a minor volcano.
Regarding pain, a helpful doctor/donor at this side explained that if CO2 gas is used in the lap method the gas can interact with body fluids to form a mild carbolic acid. This mild acid can irritate nerves, giving the sensation of pain even in areas (shoulders, etc.) not touched by the surgery. Even with the gas gone this acid and its irritation may take a little while to fade away.
best wishes,
Fr. Pat