1. This happens if the no-smoking sign switch is set to the "armed" position. When the nose gear is not locked up, the no-smoking sign goes off, so the ding is the change from on to off on take-off and vice-versa on landing. However, you will doubtless have noticed that the sign actually stays on all the time. This is because, with smoking now banned more or less everywhere, most airlines have hard-wired the sign to be permanently on if the switch is either set at "armed" or "on". So the ding is a consequence of the original system design.
2. The A320 has 6 flap settings: 0, 1, 1+F, 2, 3 and FULL.
0 = retracted
1 = 18 degrees slats
1+F = 18 deg slats + 10 deg flaps
2 = 22 slats + 15 flaps
3 = 22 slat + 20 flaps
FULL = 27 slat + 35 flaps
1 and 1+F are the same position on the flap selector lever. Selecting flap 1 on the lever always gives 1+F except when going from 0 flap to flap 1 while airbourne gives flap 1 only (i.e. slats only) - it's an approach flap setting only.
Take-off can be made at 1+F, 2 or 3.
Landing can be made at 3 or FULL.
Which config is used is airline/condition/runway/weather dependent.
We normally use 2 for take-off and FULL for landing.
Landing at 3 saves some fuel and is better in potentially turbulent/windshear conditions (more energy available for a go-around).
The flap sequence for approach:
1 at about 10NM out (when slowing below 220kts)
2 just before glideslope capture, speed back to about 180kts.
Fly down the glideslope at flap 2, then gear down.
Then 3 and 4 in quick sucession to be fully extended and at final approach speed by 1000ft above the airport.