The noise is just a vibration, which is probably caused by stick-slip friction at low rotor velocity. Most brake pads actually have a lubricant in the material to prevent this. Unless you race the car you don't need such aggressive pads. I run Repco Deluxe (NOT Metalmasters) on my 190E. They're non metallic except for what looks like some copper filiments to transfer heat. They require more pedal effort than the OE pads, but they don't, dust, squeal, "grauch" or chew up the rotors.
I even ran it with these pads in hot lap sessions at Willow Springs (big track) and Firebird in Phoenix. Even on the track the Repco Deluxe were okay. Lots of pedal travel, but they modulated well. With all the pedal travel and effort, I was almost afraid that I was generating so much line pressure that a flex hose would burst, but everything turned out okay.
For normal street use and occassional canyon carving the Repco Deluxe are great, and my projected life based on measuring pad thickness every 15K miles is 75K miles!!!