Don't presume the new battery is any good, I had a Bosch one which failed within a week.
If you have a flat battery, jump it and leave it running with the charge light on it will still be flat, well flatter, than when you started it.
All of which have potential to go wrong, unfortunately.
It's a job I would try and avoid if possible, ok you're not going to do it for the sake of it but you know what I mean.
I would suggest you get underneath and physically check the propshafts.
Even better take them off and check them, do you ever grease them?
Take one off and drive it in diff lock see if the noise is still there.
Since the fuse box has been changed you will need to do as mentioned above. Since the vehicle isn't stock it's hard to say what has been done. Operate a few things and check which one clicks, then label them or you will forget for next time.
I used the cheapest sound pads from Ebay and they worked just fine. I then used a foam insulation from Vandalised, that also worked fine.
Dodo is too expensive in my mind.
Sound pads on the inside of the door skins and foam inside the door inner trims also makes a difference.
Make sure...
Personally I think that in reality they are all overpriced. Expensive to own, run, fuel, tax, insurance and park now with emissions rated parking.
Galv chassis would be getting on for £10k fitted so the sellers would want good money for it.
£1500 tops for any in my mind.
Clean all the oil around the injectors, run the purge cycle and carefully watch for any diesel leaks around the injectors. In my limited experience leaking injectors doesn't stop it from starting a bad crank sensor or interference from a bad starter motor will stop it from starting.
Do some live...