I have a Multipla 2007 which has been working fine. However the key fob and locking have just started to play up. When I lock the car with the key fob the car locks (making the beep sounds), and a few seconds later it gives another 3 beep sounds which it has never done before and then it unlocks the car (although not all of the time). Throughout all this the key fob is flashing its little red light. I have disconnected the battery for 30 minutes and reconnected but it hasn't helped. Any suggestions what I could do?

Check that all the doors, the bonnet and the tailgate are properly closed. Does the little red light on the dashboard flash a number of times?

As WMF suggested, sounds like maybe something isn't fully latched/locked.
Try locking the car normally with the key, if it unlocks after a few seconds, then something isn't locked, or the sensor/switch for it is faulty, or you have a bad connection to one of them.
Basically, something is telling the system that something isn't locked.

Could also possibly be the key battery is getting low.
There may be a reset sequence you need to go through, there was a similar question on here recently . . .
Key fob issues

My fob was playing up for a while and I thought the battery was the problem, took the fob to bits and found that the little micro switch - which sits directly under the button - had partially separated from the board so not always making a good switch.
Out with the mini soldering iron and resoldered the connexions, re-fixing the micro switch to the board, it's very fiddly and be careful with the amount of solder you use, you only need a very small dot otherwise you'll glue the two contacts together - ask me how I know :bang:
New battery fitted and hey presto, no more problems

George