Okay, I have found a solution :D In order to enable sounds on iOS you have to play any sound once on begin touch event (or mouse down) and then all other sounds will work just fine :)
Which version of iOS is this, and does this work with a standard mouse event and sound.play(), or do you need to do anything else that is special? :) Thanks!
iOS 7.1, standard mouse event + sound.play does the job. I found some more information on this and it seems to be a common issue on iDevices: http://paulbakaus.com/tutorials/html5/web-audio-on-ios/