Maybe it was the same aircraft I was on from HAN-SGN as first part of flight to SYD. It was a Vietnam Airlines 777 and I noticed the banging noise during push back and taxiing... just a little unnerving as you like to think it's meant to sound like that. I was seated on the right hand side over the wing and it was one of the 777 they have that has 2-5-2 seating.