Just to inform others who have get this issue..
I believe I found the button 'martin' was referring to,
'SETTINGS (Save/Load/Reset)'..
when you click this, a new dialogue box opens up, on this box you click the sound box on the left, and then I click 'Reset to original RCS64 settings'.
however this did not fix the issue.
I then decided to uninstall RCS64 and re-install it, now the issue was solved and better still I did not need to upload all the tyre/throttle profiles, or anything that was saved, it was uploaded automatically..
Thanks again for the help