My 2005 E320 is doing it, also: right-front. Mine sounds like a creak, except it only pops once or twice. it seems to be caused more by side loading of the wheel, and some by braking reaction, never by suspension up-down motion or steering by itself; when steering results in side loading, though, it will pop once or twice. I can't find anything loose and the car drives very nicely.

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Providing a home for these cars:
1951 Buick Special De Luxe
1977 Rolls-Royce Silver Wraith II
1970 Rolls-Royce Silver Shadow
1986 Mercedes-Benz 420 SEL
2005 Mercedes-Benz E 320 CDI
2012 GMC Sierra 1500 4X4
1927 Pierce-Arrow Series 80
1931 Pierce-Arrow Series 43
1926 Ford Model T coupe