EDIT: The problem came back today when I first turned on the computer. So once again I deleted all openAL components (the ones supplied with the sound card's driver) and manually installed the openAL32.dll supplied by the SFML commit. Now it works again... I don't get it...
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Sorry for the double post but I guess you were right. It was a conflicting openAL DLL somewhere, just not sure where.
Uninstalled everything related to Creative and used
driversweeper to delete any driver leftovers.
Installed everything again but the problem persisted.
Went to system32 and deleted the openAL32.dll that the Creative installer put there automatically.
Then I went to the Creative's install folder which is in X:\Program Files (x86)\Creative and manually installed an openAL file that I found in this folder.
Now surprisingly any sound plays correctly now.
I don't really understand especially because this openAL's version that I installed manually is also 6.14.357.24. Well at least it's working.
Also, I have to admit I thought this was SFML's fault at the start because I've never had a problem of this sort before, so I'm sorry for assuming...
Best regards.