My iPhone 7 plus I sound muffled on phone

Hi there,

i purchase my my new iPhone 7 plus 3 wks ago and noticed every time I spoke to anyone on the phone they kept saying I sound muffled, in the distant and my voice would fade in and out. They could not hear me clearly. Anyway I call my provider ( Vodafone) who said and they had tro hearing me also, that they was going to swap it for a new one as it may be the speakers. Well I swapped and got my new phone 7 plus, but I was still having the same problem!!!! They I am not sure what I was doing but I hade a case on my phone which had a front flap cover, and when I answer a call. I would fold it behind the phone, ( like it was normal to do) well like I said not sure what I was doing but i moved the flap and left it dangling so to speak and ta dah was told what did you do I can hear to clearly now!. well I then put it back behind my phone and as I expected they couldn't hear me again, and then I left it hanging and I was clear. ta dah I had realised what the problem was, my phone was not broken or the new one but in fact as you have an additional mic in between you cameras , the case cover was infront and covered it when you was on a call. Innever had this with my iPhone 6 Plus??? But I never had a mic at the back either!!!!!!

so thought I would post this for anyone who as had the same problem , to try.

Gill