I received a response this morning and GOG was apologetic, offering a refund which I declined. I was told that they forwarded the issue to their QA team, but that "it might take a while for them to verify the issue and fix it if it's possible."
Take that as you will, I suppose. In this case, I don't think contacting support is a waste of time, so thanks to you and others who have taken the time to do so.
I've also got the same email when I logged on. I'll try the fixes they suggested over the weekend although I don't hold out much hope that those will fix it. I think it's more a job for QA as it seems that not all versions have this bug.
Thank you (and any others too) who contacted support, like you I feel that contacting them is never a waste of time :)
EDIT: Thought it might be helpful to post their suggestions in case anyone else want to give it a try;
1) Please make sure that you use "Run as Administrator" to install and to start the game (right-click on the shortcut or setup file and select "Run as Administrator").
2) Please reinstall the game AND add it to your anti-virus/firewall software's exception/trusted list. Simply disabling firewall or AV software could not be enough, since some of these software are running still in background or in services list. If you are using Galaxy, then please add Galaxy as well.
3) Please download and install DirectX Web Installer: https://www.microsoft.com/en-us/download/details.aspx?displaylang=en&id=35
Please have in mind that this will only add DirectX 9.0c to available pool of DirectX libraries, and it will not overwrite your other versions. Some games are not able to utilize newer DirectX libraries, and they require DirectX 9.0c.
4) Please try to update your sound device drivers: http://www.realtek.com.tw/downloads
If you are using surround sound system, please try to switch to stereo/2.1 sound. You should be able to do it using dedicated program to your sound device.
If you have any additional sound options enabled please make sure to disable them, or to switch your sound software to default.