I have a 06 ml 350 w/56,000 miles on it. I've been hearing a squealing type sound on it the mornings or when I start the engine cold. This noise goes away after driving for about 5 minutes. Do you all know where the power steering reservoir is on this car? Should I be concern?

 

It sounds like you are little low on fluid.
The reservoir for the power steering for this SUV is located in front of the engine, driver side. To access it, simply remove the plastic air tunnel (driver side); You will find it easily.

 

Thanks MBenz80. Located the power steering and the fluid was low, called Autozone and they didn't have fluid. Called local MB dealership and picked a quart. Filled up the reservoir and it worked great! The noise is gone.