As previously posted the ding is connected to the illumination of the exit signs (and formerly no-smoking as well). New busses don't have a 'no-smoking' switch anymore, it has been renamed 'exit' as that's the only thing which is controlled now.
The A320 does have a very clean looking wing compared to 737s, this is because it only has single slotted fowler flaps. Flap usage is nicely described in the flight patterns here:
SmartCockpit - Airbus 320 Series
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