Well... I can't find a table of Mitsubishi error tones anywhere on the net, hopefully someone else will post one on the forum.
However, it is possible that you are getting more than one error there.
The satnav gives of a single low tone "bong" when approaching a curve.
The only visible indicator is a little exclamation mark, inside I yellow diamond, that appears on the top of the map screen.
This happens if the satnav thinks you're going to fast for an approaching curve. (As far as I can see, it is VERY conservative)
You can turn that off by getting into the Nav menus:
NAVI MENU key
Type
Guidance
Curve Guidance (set to off)
The other one could be the seatbelt warning...
Any chance that you're putting something on one of the seats?
It's also possible that you're getting a warning sound, because an indicator light is faulty (I have no idea if our cars do that or not).
One way to check that is to ensure that all indicators are lit when you first turn on the car.
Similarly, could be a door open warning.
I have found that many of the warning symbols are really subtle. If you are getting the warning while stopped, look hard at all the symbols on the dash. The door warnings are indicated by a single line, on the car icon, intended to show that a door is open.
Similarly the sonar alarms are a tiny graphic which indicates the sensor that is triggering. (Little lines being emitted from the car icon)