90 200tdi wont start - weird sound

So as some of you know I have been overheating problems with the 90. In case of an air lock I have drained the system and refilled / bled the system. After letting it run for a while, i turned it off and came back to it 20 mins later to take it for a drive. I turn the key, no glow plug lights or battery light. Oil pressure light is very faint. With the ignition on there is strange constant noise I can only describe as a kind of creak or hum. The engine will not turn over. Can only presume it is some kind of electrical fault but really don't know what or the source of the noise. Starter motor is 6 months old and not a Sh*tpart.

Thanks

Sounds like a catastrophic battery drain. Starter wire come off and shorting on block?
Battery completely flat

Got any lights or interior light ?

Have to agree with above if not !!

I tried jumping it with another car and it fired right up but as you say could be a sign of something a bit more problematic. These things just seem to come out of nowhere!

If it bump starts OK I would look at your earths from battery, mine has the main one running from the battery to the gear box then on to the chassis. Defenders can't have enough earths. Try using jump cables in the mean time from the starter to the battery and see if that helps

Try connecting a temporary earth with a jump lead from battery neg to a good clean earth point on the chassis. If it works ok your problem is your earth connections.