I thought I knew all my UK terms: Boot, Bonnet, Dynamo, Energizer, Spanner, Circlip, Paraffin, Petrol, but what part is the Guard? Fender?

I searched on "C180 buzzing" and came up with 5 threads including this one:

Reoccuring Noise in C-Class!

Good luck!

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra