Nissan Patrol 4x4 (Africa)

For a few months now my 2.8 GU has been whining when power is applied. The noise starts at around 2000 rpm and gets progressively louder as speed increases, but only with the accelerator depressed. The moment I ease up on the power the noise stops. Have had the turbo hoses off and no sign of leaks or pinholes. With the turbo housing off various finger prods suggest the bearing is ok and the fan blades look ok with no sign of damage to the surrounding walls.
Should I be worried? I don't like unexplained noises but a new turbo is going to cost me the equivalent of 17000 Rand fitted. I don't want to do this and find I still have a whine.
Any thoughts would be much appreciated.

Mike

It is not easy to dignose a turbo while it is still in the car, also if you dont have a boost gauge you will not be able to tell if the turbo is working like it should.

You say you have checked the compressor wheel and cant see any damage so that sounds ok. was there excessive play on the shaft?
You can also check if the turbo is leaking where it bolts to the manifold as this can cause the noise as well.

Mike I had the exact same problem on a turbo diesel truck a few years back and as Michael said the problem turned out to be a sheared manifold bolt.

Is the pitch of the noise fairly constant once it starts, or does it keep pace with either revs or vehicle speed?

If it keeps pace with revs, it's probably engine or one of the belt-driven ancilliaries. If it's linked to vehicle speed, it's diff or gearbox related.

Thanks for your replies everyone and for being so quick with them.

I will certainly check out the possibility of a leak at the manifold. Not long before this started I had removed the EGR and fitted a blanking plate tapped to take the EGT thermocouple for a Madman unit, so will check that out too.

Peter, the noise is of constant pitch but gets louder with speed. I hadn't thought to check belts or belt driven ancillaries so will do that too. On the plus side, everyone's suggestions seem to point away from the turbo itself - just as well since replacement is an eye watering amount of money.

I should have mentioned the car has 192000 km on the clock. It has never missed a beat and this noise has not got worse in the twelve months since it started, including some high speed motorways in Europe and some very tough off road mountain tracks. (Twelve months sounds irresponsible I know, but I only use it for overlanding trips. Most of the time it is parked up.)

I don't want to lose this truck - it is one of the last of the 6 cylinder Y61's and we have been together for 14 years. So thanks again everyone.