I have got system settings -> multimedia -> audio & volume -> applications -> notification sounds
Its set to 100% and not muted.
Personally from all the reading iv done it sounds a bit of a mess. the way kde has a nice new tray notification daemon but it only work for apps built or updated specifically for kde5 like Kmail & Konversation problem is 80% of my day to day stuff does not
As i say , iv been at this problem before , many times, Im going to give up for now but probably will be back at it when i install the next thing that has notifications and it starts annoying me all over again.
Thx all for all the help and suggestions.