Welcome to the forum!
A you can imagine noise from brakes right after being replaced is not good.
I would suggest taking the car right back to the mechanic who did the work. Verify what pads and rotors were installed. There are a lot of pads and rotors on the market. Some work great and others .... buyer beware.
This sight is full of brake pad recommendations. Compare to what was installed.
Mercedes pads might eliminate the problem ... but maybe not. Sorry to sound vague but several things need to be checked out.
-The tech use any brake paste? Put on the back of the brake pad to eliminate squeal?
-What is the brand of pad?
-How many miles since this was done?
Having the tech look at his work I am sure something will become obvious right away.
Several years ago I had the rear pads replaced on the 300E. I was in a rush and let someone else do it. They *insisted* the rear pads were the right ones for the car. I would get an awful grinding/squeal only every so often, but especially coming down long grades. DROVE ME CRAZY. Took it back half dozen times.
Finally I pulled the rear wheels and the problem was so obvious: The brake pads fit the caliper perfectly and match the rear rotors as well, but instead of a slight inside arch to match the hub, they were straight across. Under hard braking (down hill grades) they would move and grind into the rear hub.
Finally, upset, I went back to show the tech ..... the shop was closed .... hmmmm.
Lesson I guess here is to find out yourself. Verify. This site is full of excellent advice that is experience and time tested.
Keep us posted,
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)