Try this for an experiment. Disconnect the vacuum line to the EGR valve and the circulating air safety valve (if it has one - this model may not). The EGR is mounted on the intake manifold and has what looks like a flexible metallic hose attached to it. The circulating air safety valve is mounted on the turbo itself towards the front of the car. Anyway, follow the vacuum lines to the turbo/intake manifold areas and these are the ones you want to try disconnecting and plugging. Try driving the car like this and see if the noise goes away.

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Jim