Key tone noises while on phone call

Hi, after updating to iOS 11.3 I now hear the sound of key tone dialing randomly when on a phone call. It does not happen all the time but when it does , the only way to make it stop is to hang up the phone and call the person back. From my understanding the person on the other end does not hear the dialing because when calling back they always say they did not hear it. Is anyone having the same problem? Any suggestions on how to fix the issues other then restarting the phone and doing a hard reset? Thanks