After second trip to dealer the mysterious buzzer chime noise was diagnosed.

The problem a blower motor, that cools the fuse box and relay housing. Blower motor apparently worn and started making noise. No problems since repair three days ago.

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2000 ML320 48750 miles
Stout 1974 BMW 2002 245,000 miles
Stout 1997 Volvo 960 Wagon 69.000 miles