Its a bad habit of people to repeat the number in the hall itself when the Bingo caller announces some numbers. Players may do it unconsciously, but it creates distraction of the other players, as they also sit close to you. In some places, the Bingo halls allow friends or families with you while playing Bingo. Its your ethical responsibility to keep quiet and not to indulge in any kind of discussion, which can disturb the harmony of the house. It is better that you should not attempt to retain the cards unnecessarily as they may create confusion afterwards. Never think of gaining any extra unethical advantage by retaining an old card as the modern Bingo halls keep track of each card using latest methodologies.
Its always advisable that you never become louder except calling Bingo as loud speech may create exultation in the room, which restrains players from listening to the announcements made by the caller. So, be matured and play Bingo in its true spirit.