Hi guys, just an update I forgot all about it. The noise somehow disappeared entirely - not sure if something was loose or what but it hasnt happened for over 8months now. I have however recently acquired a new noise - between 1500 - 2000 revs it is like a chirping noise. Mechanics have tried removing drive belts but noise is till present with belts removed. It appears loudest behind the dash and will appear to speed up as the revs increase. Mechanics have gone over the engine bay with the hearing scope thingy (sorry dont know the correct term) as i've held the revs at 1500rpm, but cannot hear the noise. Conclusion is it must be something behind the dash but for the life of me, cannot figure it out. The car had sat idle for 4.5 weeks while I was away, after which the noise was first noted.
Presently scrolling around the forums to see if anyone else has had this issue...
in this video is the audio I recorded from sitting in the drivers seat. Vehicle is a D40 Navara 2011 Spanish built, auto with 166k kms. EGR is blocked, after market hotpipe installed and catch can - all installed well before the noise appeared.
At those RPM the major change in the engine's operation is the turbocharger reaching full RPM, which also means full flow through the exhaust. You might find small black sooty deposits around part of the exhaust manifold, particularly the part that meets the turbocharger (although don't ignore the EGR pipe). Gaskets can become thinner and act like a reed in a clarinet say - I had that exact problem, and mine occurred mostly around 2,000rpm.
Otherwise it would be prudent to check that the pulley for the alternator is firmly attached to the alternator, and the radiator fan itself doesn't have any cracked blades that might be pulling forward at the higher RPM and scraping the back of the radiator.