I have downloaded the update 4.3 from United Kingdom - BTU via Kies and since then have severely distorted headphone and speaker output. So bad it just sounds like a dieing dalek. Phone was stock 4.1.2 previously and all working perfectly.

I have repeated the firmware download / factory reset 3 times and there is no difference.

Also (with no apps installed) the screen randomly turns on (screen lights up) now and then when the phone is being moved. Not when sitting still on the desk. I think this may be related to the wifi (slow internet message possibly)..

Calls are fine, it is purely headphone and speaker - any app that produces sound is now unlistenable.
Via Bluetooth in car and wifi direct on Samsung TV all is fine.
I have searched all forums and not seen anyone report the same issue.

Anyone any suggestions ?

Wasn't a good move - battery previously would last to around 34% before I went to bed. Now its 35% by 3pm in the afternoon - yet my colleague who did the same update on the same day has no obvious issues at all other than not being able to share gallery pictures. I don't get why it should affect different phones differently.