You're absolutely right.
I know this might seem pedestrian or patronising especially because Microsoft have in their troubleshooting but it's not intended.
Have you tried getting a vacuum cleaner on the microphone areas of the 1020. Poor sound quality looks as though it has something blocking it, as opposed to it cutting out. I only say because I once had this problem on a few previous non-Nokia phones. And
it was lint and dirt inside either the headphones jack/socket,speaker, mic area etc. I must be a dirty person. haha.
Once I thought my very expensive headphones were broken. I accepted it. Then I managed to get some food in the headphones socket of my phone and couldn't get it out. So I used a pin to crumble it and pull it out. Instead a relatively large piece of dirt
came out and the headphones worked perfectly.