I've 2003 c230 Komp with 70k miles.
I'd my mechanic replaced front pads and rotors with mercedes parts and it started to make some noises.
The noise sounds like low abrasive - ones come from worn out pads.
This only happens at 40-50mph and semi-hard braking.
The mechanic took out the both pads out and they can't figure out where the noise is coming from. The rear pads and rotors are fairly new.
I was wondering if there is a certain direction that the pads must be fitted or the pads are bad ones and must be replaced.
If anybody had similar problem, let me know it would save me a lot of time going back to the mechanic who can not figure out where the noise is coming from.

 

The finish of the rotor can cause a rotational noise if it not treated properly. Also if a coating is placed on the rotors during manufacturing and they do not remove it before install you can get some noises. If that is the case the coating can become embedded into the pad and remain noisy until they were a bit.

 

Thanks fnc for your info. We had our from brakes pads replaced by dealer at 30k miles and we never had this problem at that time.
But there is no noise when there is slow braking. The noise only develops when there is semi-hard braking on or about 40-50 mph. It sounds like a low abrasive noise. There is no sharp or high pitch grinding noise like when your brakes wear off.
My mechanics have taken the brakes apart and they've used sand paper to make the pads smoother. After this procedure, brakes have reduced the noise but still make annoying noise. Do they need to replace with a new sets of pads?

 

Sounds to me like the rotors are at fault. From what you are describing. They will make this type of noise if they have a rough surface. May look smooth to the eye, buy to touch you will feel what I am talking about.

 

My mechanic have replaced with new rotors and pads and the problem went away.
They said it was either problem with rotor or pads and they did not wanted to take a chance so they ended up replacing both parts.
Thanks fnc for your info.