High pitched whistling sound from exhaust at idle c220d W204

[gabeyeap]

As above, does anyone know what that might be? I’ve attached a video below and you can clearly hear it!

Untitled Project - Kapwing

Video made on Kapwing

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Thanks everyone! The mechanics booked it in for a look next week, just wanted to brace myself for cost to repair and seriousness of problem in case it is a big problem!