A117 micromax magnus suddenly mic volume went down

I have been using my a117 for over 2 years. Suddenly the phone mic volume or sensitivity has gone down and no one is no longer able to hear me clearly over the other side of the conversation on my phone. I wanted to know if this is a software or hardware issue. And if it is a hardware issue how can I fix it? I want to clean the mics by opening up my phone. Can anyone provide me a service manual to this phone that tells me how to open it up exactly...... Please I need help with this issue...