MB monoblade wipers seem to be notorious for squeaking and skipping. There are a number of potential solutions:
1) As kestas says, be sure you really clean the glass well with Bon Ami or similar product. Some also recommend using lacquer thinner to remove wax and grease deposits which lodge in the inevitable pits MB windshields acquire.
2) If the blade is not perpendicular to the glass when in mid-stroke, it may be noisy. Turn the wiper on with ignition on, then switch ignition off while blade is still moving. You can then manually put the blade in the middle of the windshield and see if it is exactly perpendicular to the glass. If not, bend the arm carefully using 2 crescent wrenches.
3) Keep the chrome plated shaft of the mechanism lubed. You will see this shaft if you lift up the rectangular plastic piece at the base of the wiper arm. Use a little silicone grease, or, as some suggest, ATF. Needs to be done periodically.
4) Check the hinge points on the wiper arm itself (by this, I mean the piece with the spring). If this piece wears excessively, it'll allow excess "slop" in the assembly which can cause noise.