Thanks again, Scotty.
It's the BMN 170bhp PD engine in my car.
Thankfully, my turbo seem to be pretty quiet...
I've scoured t'internet and read multiple forum posts that point at:
- Pressure Converter Valve / Boost Control Solenoid (N75 valve?) on the bulkhead
- Perforated diaphragm in the Vacuum Actuator/ Turbo Actuator ?
- Intake Manifold Flap Actuator
- Perished/split inlet manifold gasket
... As the main culprits?
Anyone offer any advice on which is the most likely? Thanks.