Possibly from the dome lamp area? There is a small electric motor that pulls air across the in-car temp sensor(a/c system) & many of these do make a buzzing noise (warranty??).

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MERCEDES BENZ MASTER GUILD TECHNICIAN (6 TIMES)
ASE MASTER TECHNICIAN
27 YEARS DEALER M.B. Shopforeman
190E 2.3 16V ITS SCCA racecar