Octavia III - 2013 - MIB1 - Bolero (FW:0490) with Apple iPhone 6S (iOS 11.3)

 

This is a problem that has started recently (before the latest iOS update, which hasn't made any difference). When I am on a phone call the other party's voice is quiet and has a background hiss (white noise) whenever they are talking (but it is not present when they are not talking). 

 

When I play music via Bluetooth it sounds fine - no hiss at all.

 

I have had my iPhone replaced by Apple (amazing service - well out of warranty) on the back of this, but that didn't change anything. I have tried resetting the Network settings, and I also tried reinstalling iOS on the previous phone, but nothing has affected the problem.

 

I am very puzzled by this - there is no problem with voice quality on calls when the iPhone is handheld, and as I say above the sound quality over Bluetooth is fine, so I don't think it is either a Bluetooth issue either end or a problem with the phone part of the iPhone. What could be causing this? Does anyone have any clues, or have experienced this before?

Pair a different phone and try it with that.