Horrible loud buzzing noise

[Sony_Guy]

Hi,  yesterday my Sony z4 made a horrible buzzing noise,  louder than music on full volume, when I was reading the screen,  which continued for a few seconds until I hit the off button.  This happened a couple of times, but otherwise it worked normally.  The machine installed it's latest update after this,  but this morning the buzzing happened again.  

Does this indicate a fault, do you think? I rely on the z4 for work,  and I do like it.  Wouldn't want to be left suddenly without it if it fails. 

Thanks 

Guy 

[thedailycommute]

I have a Z2, updated a couple of weeks ago to the latest version of Android (6.0.1) and suddenly, out of the blue, it also started to buzz extremely loudly. This happens if the media volume is set to zero, or the phone is in "do not disturb" mode, and I play a video, for example In YouTube.
Everything was working perfectly until today, in fact just about 30 minutes ago!
The only recent update was the update application itself, nothing else has changed.

Has anyone else begun to experience this problem?