Freelander 1 not starting occasionally

Freelander occasionally doesn’t start - Even when it’s been running a while so don’t think it’s the glow plug but I have no idea to be fair. It’s a 2003 freelander diesel.

Occasionally it won’t start, just makes a loud whirring sound (starter motor trying to crank the engine maybe?). So I Give it a few mins and it starts after I’ve tried the ignition a few time’s.

I know I’m meant to “heat the coil” with diesel cars and wait a few seconds before starting the ignition and I’ve been told it’s maybe the coil what needs sorting, but I’ve also been told it’s not the coil as the weather is to warm and it occasionally happens when the cars warm and has been running for a while.

When I lifted the bonnet up with the key turned all the way to “electrics on” I heard a very slight noise then it stopped and as soon as that very quiet noise stopped I turned the ignition all the way and it started. What would this very quiet noise be under the bonnet? From what I’ve read so far it’s either the fuel pump (solution I was told is knock it with rubber mallet etc) or it could be solenoid sticking (soloution I was told is replacing starter motor)
Any help would be appreciated, please keep answers simple as I know very little about cars inner working so I just want to be able to tell the mechanic what he needs to fix so I don’t get my eyes taken out asking him to identify and then fix the issue.
thanks.

As you say - its not the glow plugs if it also doesn't start when warm, and shouldn't really be needed in the UK at this time of the year.

The 'slight noise' could be the ABS priming or the fuel pump noise which isn't under the bonnet - its under the rear wheel arch (maybe also another 1 in the tank?)

Your problem really depends on that "loud whirring sound" is - if the noise is occurring and the engine is not turning over, then as said, my take would also be the starter solenoid is not functioning and engaging the starter. A mechanic will probably replace the starter, I dunno if the solenoid itself can be fixed easily. If the engine is turning over - then it could be various things. "Various thing" could be cheaper or a lot more expensive than a starter, but probably a lot more diagnosis. If it was mine, for an easy life, I'd be hoping it was the starter.

If is was the starter the car would not crank it would just click, or no noise a all, then it would be starter, which is a £10 fix a about 45 minutes work contacts and plunger,

https://www.ebay.co.uk/itm/ROVER-75...AIR-KIT-228000-7801-or-NAD101500/252158920680

The wirring noise, if the engine is turning over then starter ok. If your not sure if it is the engine turning over then try it in gear. If the engine turns over it should move the car forward so make sure clear first!
Sounds like failing fuel pump, not sure where as earlier ones were in the tank.
Later under the wheel arch at the back drivers side (UK).

I thought that some of the earlier models had a low pressure fuel pump in the engine bay? Not sure that would apply to Dean's 2003 model.