Hey guys its a very stupid idea..but try it..it worked PR fectly for me....
1st of all remove all the back covera on ur phone.. And see where the mic is located..bith the primary as well as the secondary...as u find them..just try and suck the mics with a bit of pressure...it solved my problem..as my rubber cover was a bit loose frm inside..sucking it created a pressure of air..which pulled the cover more inside..hence my echo problem was solved...without opening my mobile phone...try ur luck guys..