transmission help!!!!

[playfuldodger]

hi guys.. dont post much cause usually dont have any problems to post about but in need of help and advice please.. i got a 2005 3.0d auto and when im driving at low speeds i get a rumbling noise i suspect from the transmission or 4 wheel drive sytem.. this does only happen at low speeds and i have no other issues when driving and works through the gears perfectly.. it is worse when engine is cold and sounds more of a grinding whirring noise if that makes sense... i have spoke to a gearbox specialist who will fit me a recon box and four wheel drive box for just over 2 grand but he is not prepared to commit to it resolving the issue and therefore i am sceptical about being relieved of 2 grand for the problem to still be there.. so if any of you guys have any feedback or input it would be gratefully appreciated