Sound problem with iphone 7 during a call

I have 2 iphone 7 and i have a problem with the older: sound is bad during a call but sound is ok with speaker ON.

iOS is the last 11.2.5

For the other i have no problem.

I tried to exchange sim card and configure the iphone with with same options but nothing change.. the older has always sound problem.

I will go to the store for a repair and would mike to know il someone has the same problem...