***UPDATE: Turns out it was the secondary air injection (SAI) pump that was on the verge of dying. A simple part replacement corrects the problem. ***

My 2005 Audi A4 1.8T recently started making this weird yet loud whining noise on cold startups. The sound goes away once I start driving.

I've managed to isolate the area it's coming from (just below the headlight on passenger side) but have no clue what could be causing it, or whether I should be worried.

Any help is greatly appreciated! Thanks.

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