Turbo whine on engine unload after blue smoke discharge

Hello all
I have a 2006 D40 YD25 Spanish built Navara which has developed a turbo whine when you come off the throttle and unload the engine. The whine sounds like the turbo noise created when you deliberately disconnect a wastegate valve on a turbo and and there is no wastegate to release the overpressure through the turbo.
The whine started after I was driving up a fairly steep road at 60kph with the engine under load and the car suddenly slowed for a second and a large amount of blue smoke was discharged out the exhaust (saw it in the rearview mirror). The engine is still going ok and the boost from the turbo seems normal (car has over 300,000 kms on the clock) as it still accelerates ok although the fuel economy has gotten worse, probably about 50 to 60 km less per tank.
The noise doesn't seem to be there if you rev the engine whilst sitting in park and only occurs when the engine is under heavyish load and you come off the throttle quickly while driving.
From some of the research I have done I though it might be a failure of the vacuum actuator on the turbo.
I'd appreciate any advice anybody has on this issue.
Thanks

I'd be suspect of the turbocharger itself.

Under load, there's a pressure on the bearings caused by the impeller pulling itself "forward". It's not a huge pressure, but it is there. Once unloaded, the main shaft can relax and the impeller can rest. It might be starting to rest on the rear of the housing.

There's a REALLY easy way to tell. You'll need a clean finger and a bright light.

Find the turbo hose that connects to the baffle on the side of the engine. Loosen the clamp and remove the hose.

Now, wipe your clean finger on the inside of this hose. Look at it under the bright light.

If you see silver sparkles, your turbocharger impeller is rubbing on the housing (in your case, likely to be the back of the housing and not the front).

If you see gold sparkles, your turbocharger's bearings are badly worn.

If you see NO sparkles, the intake side of the turbocharger is probably ok. You should replace the hose and now check the impeller shaft. Remove the hose from the INTAKE side of the turbocharger and wiggle the impeller shaft. Any movement here is bad (except for smooth rotation).

You CAN put a second hand turbo in, but there's obviously a risk of the same thing happening.

A brand new turbo from Nissan is upwards of $4K. You might consider this if you have shares in Nissan Motor Co, or you've won the lottery.

A brand new GENUINE Honeywell Garrett 2056V turbocharger from a mob in Brisbane (I wish I could remember their name) will charge you south of $2K (I think I paid about $1400 a couple of years ago).

It IS possible to buy a rebuild kit. These kits generally contain a new set of bearings (perhaps even a full shaft), and new seals. The problem with these kits is that they don't address wear of the housing, ONLY the interior of the bearings. Still, for the money (I've seen them for under $100, example below) you might feel happy enough with the risk.

https://www.ebay.com.au/itm/394857337161

Tony
Thanks for the reply. Could you please clarify a couple of things for me as I am an electrical engineer and other than doing things like fuel filter changes and drive belt replacements I have precious little experience in the engine bay of the Navara and none on the turbo side of things other than a general idea of how they work and knowing the location of the turbo on the RHS of the engine as you look at it.

"Find the turbo hose that connects to the baffle on the side of the engine"
Is this on the air or exhaust sides of the turbo and where is this located?
"Remove the hose from the INTAKE side of the turbocharger"
Is this the air intake or the exhaust intake?
Also I found this mob in Melbourne selling YD25 turbo's

https://cctturbo.com.au/collections/nissan-navara-d40-turbo-charger

I could afford to buy the $800 model (as long as it is compatible) and get a mechanic to install it as they claim the turbo is bolt on and ready to go. I'd appreciate any thoughts on this replacement.

Thanks again for your time