S-max Mk2 2.0 Ecoboost What's that noise?

This sound is heard inside when you take your foot off the acceleration pedal. It does not always occur and it is difficult to determine the conditions in which it appears. The noise can be heard in about 25s. Any ideas?

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Dzwiek powietrza uderzajacego o łopatki turbiny. Noramlne zjawisko