Microphone issue with iPhone 6 Plus.

Hi,

I am using iPhone 6 Plus (64 GB) for nearly one month. It's a brand new phone. I am using Airtel network ( LTE / GSM ). When I make a call, the called party complains that sound received through their handset's earpiece is Cracked / Noisy and some times not audible at all. Same thing happens when some one calls me. On my side, I don't find any problem. It's only on the side of Called or Calling party. They can not hear me clearly through their handset's earpiece as well as the speaker phone. This has been observed on different Networks and different Handsets of the Called / Calling party. Initially I thought it may be some network issue either from my side or from the Called/Calling party. I faced the same problem even after replacing my Airtel SIM card with another operator's SIM card. I have not contacted Apple Service Center so far.

Any suggestions will highly be appreciated.

Thanks.