All is fine otherwise and the steering system quiet at idle, fluid is at max line. Should I try the Pentosin 11s? I already tried adding the Lubrizol and it made little difference. Not sure if the noise come from rack or from pump.

__________________
2008 S550
2010 GLK350
1997 E420 (retired)
2005 CLK500 (retired)

Can be the reservoir, has built-in filter area.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

I will have to check... Seems you would be leaning towards the pump rather than the rack being the cause?

__________________
2008 S550
2010 GLK350
1997 E420 (retired)
2005 CLK500 (retired)