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You can view this related issue thread as yours. Hopefully it can help you.
http://saabworld.net/showthread.php?t=28212

Have you tried checking flow of air or oil, or foreign material in the bearings? Because one of them can lead the noise. Also, you can check wastegate actuator if it might be stuck open and check...

Have you solved this issue yet? If not, you try checking the rear fog, the rear running lights or reverse lights too. Also, take a look at the wire or connection if there is anything break.