@GrumpyGel is the expert there.
lol.
You do need a finely tuned ear to pick out problems though.
If it goes
BANG BANG BANG BANG this is the first symptom that something is up.
Once an issue has been diagnosed, the solution is very simple.... throw money at it, and quite a bit more than £3.10.
Actually, the first symptom I had was the car "not feeling right" - wandering a bit, steering not quite as precise as usual. Nothing much just a feeling. We were on a road trip though with visitors, didn't seem to dramatic, so leave it till after they've gone. Then after about 400kms, a rattle developed, thought the exhaust was falling of its mount at the back. Then a k or 2 later it went BANG.
I believe the "not feeling right" was a tyre low on air. When I got out of the car, the RHR tyre was rather hot and severely worn. We had navigated a lot of very twisty roads, mountainous roads and flat open roads in that 400kms and I didn't notice anything really wrong until the rattle.
The banging was gears slipping in the IRD. I pushed the car off the road and every 2 meters or so there was a horrendous metallic bang.
I didn't test the VCU, but presumed it had been cooked and was U.S.
The IRD case didn't shatter, it was fully intact. Oil was grey as. Bearings toast and I believe gears damaged. On removing the props and taking it for a drive round the block, this is what it sounded like...
Obviously no good. A replacement IRD & VCU here was going to cost about £3.5k - so not an option. Getting a VCU, IRD recon kit (bearings, seals & cooler) and Crown/Pinion gear set shipped from the UK was the only option to get it back 4WD and still to expensive. So I got a recon kit sent over, got a diff shop to install it and while they were doing that to remove the crown gear off the pinion. I put it all back together including rebuilt IRD and original pops/VCU. Its been running fine for 5 years since the rebuild - but it is 2WD.
In the UK you may be able to get away with removing the IRD rear pinion and installing a blanking plate. Over here (and I believe NI) that mod would have required certification ($$$). Also I'm sure the prop dampens the engine some.
My experience is why I'd never own a 4WD Freelander without a TPMS system fitted. It would have told me there was a problem way before it became an issue and I'd have never had that pain.