I tried yesterday all the methods described on this thread, and to my frustration the echo refused to go away, when i was ready to give up and after three failed attempts, i opened my phone one last time to take out every piece of rubber.... and then I noticed something was wrong with the original rubber that covers the noise reduction microphone, it did not fit tight, i checked it and notice the opening that cover the noise reduction microphone was not big enough for the actual microphone to fit in completely, so I opened it just enough for it to fit tight, I took all my rubbers out and to my joy it did work. I have been testing the phone the hole day and have had no eco at all. So for those of you that the previous methods haven't worked try this , maybe you are lucky as was I
Good luck to everybody.
Picture 3 shows the 2 components that's interfering with one another. "A" is the NC microphone sensor. Be sure to check that the sensor is properly inserted into the rubber sleeve covering it.