Thank you. Well, like I expected, I had had to reset my iPad again, and now my original sounds are back. Apparently my iPad made other sounds then the settings said. So I had to enter my password for WiFi again, I had to reset background, switch off bluetooth, check locationsettings, reset keyboard, etc; great fun.
Added: I just walked through all my sound settings, and the sounds my iPad suddenly started using (almost cinematic, spacious and rich sounds, high quality, but far too rich and theatraal to my taste) are not in the settings, I can't reproduce. Seem to me almost a hidden new feature, easter-egg?
Remaining problems; iPad doesn't place cursor at end of sentence but selects last word, about 20% of the time Safari doesn't respond to touchscreen/screentouch. Safari stops suddenly and unexpected. Video's keep playing after closing webpage, big empty white screen when entering search string, paste bar does not appear when touching screen, after cut or copy selected text, text appears not to be cut or copied, previous cut or copied text is pasted, etc. etc.