I too, hear the same noise when I get going first thing in the morning with my 93 300E. I probably should have investigated it since it has done so since I bought the car at 72K miles.

Good to know it's a normal function...

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car