I just replace my old rotor to zimmerman cross drilled. I also replace the brake pads with mintex red box (I saw on this forum that mintex is good). After about 1 month, it starts making high-pitch sound when I press the brake at low speed. Now I am thinking of getting EBC greenstuff pads, anyone has any suggestion?

Thanks.

There exists an Audi Technical Bulletin on this exact issue.

In summary, it states as follows:
1. Take apart your brakes and clean all of the contamination (brake dust, dirt, old synthetic brake grease, etc.)

2. Pads: Deglaze the pads with a rotary sander at 80 grit until you get to virgin brake pad. Bevel the edges of the pad to allow for better bedding, i.e., the edges of the pad cannot dig into the rotor until the rest of the rotor gets bedded.

3. Rotors: Sand the rotor with a rotary sander at 80 grit until you get a nice clean rotor with a slight rotory sander pattern.

4. Caliper and Caliper holder: Brush and chemically clean as well as possible.

5. Assembly with synthetic brake grease: apply brake grease liberally to all places where the back and sides of the pads come into contact with the caliper and caliper holder. HOWEVER, DO NOT GET ANY BRAKE GREASE ON THE FACE OF THE PAD OR THE ROTOR!!!!

6. Bedding: Besides braking very gently during the first 500 miles after assembling the brakes, on your test drive, do a very deliberate routine of braking consisting of straight gentle braking from 40-10 several times, 50 to 10 several times, and then 60 to 10 several times. This should get the pads and rotor to exchange material and create the composite substance that actually stops the car.

7. EBC Brake pads: Due to their kevlar composition, they run very hot compared to Mintex and other brake pads. Thus, you need high quality rotors, otherwise you will suffer the same problem I did: hot spots on the rotors. I used ATE Powerdiscs with EBC's and the combination does not work, because the Kevlar on the EBC's combined with the continous slots on the ATE's creates too much heat for those rotors. The EBC's worked okay on the smooth OEM rear brake rotors. They have incredible bite and work quite well.

P.S. I had developed a low speed brake squeak over several months. I finally got sick of it last week as it became louder and did exactly what I described above. It worked perfectly; No more squeaks and very solid brake feel. While the pads had a bit of a glaze, I think my problem laid in that the synthetic brake grease had simply worked itself out and/or washed out over time.

The easiest and cheapest solution is to buy de-squealing grease for a couple bucks and put them on the back of the pads.
Or you can buy A8 pads straight from the stealership. They're identical to A4 pads, but they have some cushioning on the backs. Not really worth it since they're twice as expensive (like $95)