Disco 2 td5 2003 2.5LTD

I took it off roading yesterday for the first time and after I could not make it up a rocky slope I stopped half way up and put it in to low range. Before I did this the engine cut out a couple of times (stalling up hill and sucking up a lot of fuel with it and briefly displaying the oil light as I can imagine pressure was lost.

Once I put it in low range I was able to slowly climb but ever since the disco stalled twice there has been a light whistle noise coming from the front (sounds like under the bonnet) (More driver side (LHD)) but maybe thats just because im sitting to that side.

It is not made worse with acceleration and when I am traveling at a good 50klm ph I can not hear the sound over the engine but when stationary again the sound is audible.

The sound is present from when I turn my key once (ignition but not starting the engine and stays constant) almost sounds like the fuel pump whistling up but stays present and comes from the bonnet.

Sound is now present in either transmission modes.

No loss in power or any other issues I can tell at this point....

Any ideas?