From my own experience:
Whining sound is down to excessive play in the bearings on the turbo impella. Happened on my PD 140 after 3.5 years and 65,000 miles. Its extremely unlikely to be a hole in a pipe or somesuch as turbos need to be entirely sealed units to function and if you had a hose blowing, you'd have zero power remaining.
I diagnosed the same
problem on mine in June 2009.
Gradual decline in power to about 70% of what it should have been - dont really notice as it happens so slowly.
In May 2009, i was coming off an island, powering out of the turn in 3rd and POP!
Turbo popped, impella sheared and drew oil into the engine, cue large amounts of black smoke.
Recovered to independant garage.
Sourced recondtioned turbo from turbo technics: £500 + vat (new from Seat is £1300)
Fitting at local Garage: 200 + Vat inc new gaskets and seals.
Total Cost: £822.50
Did a lot of research on this over the cause of the year that it took my turbo to blow. No one can really repair the bearings on the turbo, as the units have to be balanced and there are very few places with the equipment and expertise to do this. Turbo Technics are one of them, but they'd rather swap out the turbo.
There is no set time line on how long it will now take the turbo to pop once you are hearing the wine from worn bearings. I have heard storied of anywhere from 2-3 months to over a year.
Change your turbo before it pops. When mine went (i didnt change it because i was considering selling the car) it drew most of the oil thru my engine in just a few seconds! The sump was almost dry so i was incredibly lucky not to sieze the engine!
Additionally, the entire exhaust system was literally flooded with oil. When the turbo was changed, the garage had to leave the car idling for THREE hours to burn off this oil in the exhaust system. Again i was extremely luck not to have to need a new CAT or exhasut due to oil damage.
