"Duly noted" is an everyday expression which does not literally mean that you are taking down notes!
"Duly noted" means that you have become aware of the matter and have mentally noted it (and will deal with it if necessary). In short, you have taken note of the hint being given.
Note: Duly noted should not be confused with Point well taken.
1. The India Study ChannelWebmaster thanked the member for alerting him about the fake account and said that it was duly noted and would be dealt with right away.
2. The chef duly noted the diner's complaint of the curds rice being sour and immediately sent a fresh dish of rice to his table.
3. While the staff felt that their work was not being adequately appreciated, actually the Boss duly noted which of them was efficient & diligent and planned to give them a special bonus.