Apologies for not replying sooner.
The day after my last post things got worse, all audio output sounded as if being passed through a delay pedal. This was across all apps and RB still had Left output only.
I decided to perform a Windows recovery and that cured the audio but also messed up my log in details to this forum. It has taken until now for support to get me back!
So the problem is not solved but has gone away.

Thanks for your help.

Vintage