Nigel,
It might be ASIO / WASAPI conflict in your BIAB Audio Settings. You can try changing things there.
Most of us do not have issue with ASIO being selected in BIAB and auditioning demos. But some do.

Some people swear that selecting MME in BIAB Audio Driver settings is the silver bullet... I don't know. Try that.
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If that doesn't work, to troubleshoot I would start by:
1)Close BIAB
2)Go to the drive where "bb" folder is located and to bb/Demos/RealTrack-Demos
3)Scroll down the list to WMA files and try to simply play it using Windoz.

If you hear the sound most likely it is some sort of audio driver conflict (and maybe you should try highly praised MME as solution)