Buzzing / humming in speaker intermittently when making calls.

we just received a replacement i5 for my husband. don't know if this is the same thing we're talking about. when he makes an outgoing call, the phone has a strange "vibrating" sound. no incoming anything...no calls, texts, mail, nothing. we reset everything. then we went to the local Verizon store and they heard it and tried looking it up too but can't find anything either to match this problem. the closes apple store is 35 miles away and this doesn't happen every time. I hate to make an appointment, drive there and not have it happen. I've seen people talking about the cases causing a problem but this is more like when you have it set to vibrate except the sound is in you're ear.

Yes, my apple 5S is doing the same thing. I have a case on it, and thought that this was the origination of the vibration, but when I pinch the case firmly to the phone, it still vibrates annoyingly when I am making outbound calls. Like you, I thought that I was receiving a text or another phone call or something while I was dialing out but after checking for missed calls and text, determined that this was not the case and it happens every time. I have a symbol on the top of my phone which is a symbol of a phone with two rows of little balls under it, and I'm not sure if that is something that indicates this feature. I have looked all over for a setting that would allow me to turn this off.

Help!