After unlocking the drivers door and opening it, I hear a low level whirling noise coming from the rear end of the car.

I have checked this out further and it seems to be in the area of the petrol tank. This noise stops after about 4 - 5 seconds.

If I close/lock the door and open again I do not get the noise.

Also if I open, first time, any other door than the drivers the noise is not there.

It's got me baffled, but some one will know what it is - hopefully.

That is most likely the fuel pump priming.

As Pete says..Its the fuel pump..Perfectly normal

My old merc used to make a loud noise on the fuel pump, sounded like one of those electric aerials, worrying the first couple of times I heard it.

As Pete says..Its the fuel pump..Perfectly normal

Yup, it does sound like it could be that, it's certainly in the right area.

Thing I don't understand, is why opening the drivers door would set the pump off (priming up I suspose)

I would have expected operating the inigition key would have done that , but who knows???

Yes, it's the fuel pump. I asked the dealer about it the first time I heard it, this is what he said:

A fuel pump is used to supply fuel to the fuel injection system or carburetor, depending on the year of the vehicle. Older vehicles use a mechanical pump to deliver low pressure fuel to the carburetor, while fuel injected vehicles require an electric pump capable of the high pressures required to make the system work efficiently. A fuel injection system is more efficient than its predecessor the carburetor and can better operate in extreme conditions, while becoming more dependable at start up.

Yes, it's the fuel pump. I asked the dealer about it the first time I heard it, this is what he said:

A fuel pump is used to supply fuel to the fuel injection system or carburetor, depending on the year of the vehicle. Older vehicles use a mechanical pump to deliver low pressure fuel to the carburetor, while fuel injected vehicles require an electric pump capable of the high pressures required to make the system work efficiently. A fuel injection system is more efficient than its predecessor the carburetor and can better operate in extreme conditions, while becoming more dependable at start up.

Thanks for reply. Yes I fully understand that now.

BUT what I don't understand is - " Quote"

Thing I don't understand, is why opening the drivers door would set the pump off (priming up I suppose)

I would have expected operating the ignition key would have done that , but who knows???

There must be many cases where it is necessary to open the drivers door and not start the engine,

so why fire up the fuel pump at this stage.

It's got me baffled, but some one will know what it is - hopefully.

May be worth checking the fuel pipe connections to the pump. On my Meganne they were just push fit, and the ones to the fuel filter under the car once started leaking, but just needed pushing back on. If the connections are allowing some air into the lines, which may be by being disturbed during door opening/closing jolts, the pump would probably operate to maintain the pressure.

The low pressure fuel pump is activated by opening the drivers door. If you look up instructions for changing downstream components in the fuel line you will find warnings about not opening the drivers door !