Thats the motor you wanted!
The sound you hearing in the gearbox is Harmonic resonance created in the relationship between the Nissan HD 5 Spring Clutch, the characteristic pulses of the TD42 and the gearbox itself. Some people call it Gear Roll-Over, but its actually resonance. There is no damage being caused at all , and there is NOTHING you can do to stop it. I have researched this to the ends of the earth, and there are millions of threads on this on the web. I personally hate the sound, but have accepted it as commonplace with the 4.2 patrol diesel. I was originally very worried, but after my findings i leanred that there is no iddue at all and no damage being caused.
Both my Patrol TD42 have had this sound.
Anyway, stoked you got your pickup,... you gonna enjoy this thing for a long time.
'07 Patrol Pickup TD42 N/A,285's KM2,3" Lift,ONCA Bars,Warn High Mount,Alu Canopy, and some other Stuff.