Screeching Turbo, any ideas ?

[Darryl]

My 96 Aero ( manual ) has started to make a sort of high pitched screech when i start to accelerate hard and am well in boost.
I am certain that the noise is from the Turbo and it sounds more like an air leak than anything mechanical.
The car still feels fit and i cant see any loose pipes after a QUICK check.
Has anyone got any ideas what it could be. It has just come on over the last week or so .
The only thing that i have done in the last couple of months is fit an Abbott downpipe. It looks to be on properly still and all the bolts are tight. The exhaust is not leaking anywhere.
The boost gauge indicates that all is still normal but this noise is spoiling the car.

Thanks Darryl

[cdcarlsson]

Loose or more likely missing exhaust manifold studs. Usually the top right as you are looking at them. It allows exhaust gasses to escape under pressure. I've had it on two cars, the first had a cracked stud that was in place but doing nothing, the other car had a missing stud that had broken and fallen out.
Eventually the soot coming out will leave a stain on the block.
Nick.

[misleading]

I had this with my 2.3 FPT just after I got it and there was one missing and one broken stud. It is now quiet and boosts a little better. You'd need to take the whole manifold off, repair the damaged studs as required and clean the head and manifold before re-assembly with a new gasket. Broken studs can be a pain to get out.

[Saab qualified]

It may also possibly be the turbo air impeler scraping off the air intake shroud ( aluminium unit ) in the turbo unit itself. If it is this then just leave it alone and try and live with it. Commonly known as turbo whine