Why does my iphone 6 produces a static sound on the other end when making a phone call using speaker?

Hi,

I’ve just got a new iphone 6 that I have used for approx. 1 month, about a week ago, alot of my friends and family members that I have called has been complaining about a really loud, annoying static noise when receiving a phone call from me. After further tests and observation, it turns out that this only happens when I make call using speaker phone. I have tried restarting my phone, turning on noise cancellation, without any luck of fixing this issue. I tried recording my voice using voice memo and it produces a clear recording of my voice. I also tried ringing my other iphone to test and observe what people are talking about the static noise, it sounds like a really loud static and pinging sound coming out of the phone. This does not happen when I am calling using normal mode, as soon as I switch to speaker, the noise will start again and no one could hear my voice but the static noise. Please help if anyone has got a solution to this issue. Thank you very much.