AirPlay works with MacBook - but not with iPad or iPhone

My MacBook connects to my speakers connected to an Airport Express via iTunes and streams music perfectly well, but I'm having big issues with my new iPad.

My iPad can see the Airport Express speakers, and seems as though it can establish a connection; the interface appears to think that it is streaming to the speakers, however, no sound comes out...

Tried to stream audio to the Airport via the iPod app, YouTube app, etc. from the iPad, but no luck...

I've tried restarting the Airport, erasing all settings, doing a 'hard erase' of settings via the reset button on the Airport, turned off all network devices bar the iPad... But nothing seems to work...

My MacBook can still send music perfectly well, so I'm very confused which product is the issue, although I've tried to use a friends iPhone 4 with iOS 4.3.1, and that doesn't work either.

So, in short, there's a problem with either iOS, or my Airport Express...

I can see a few other people are having issues with AirPlay, however due to the fact that my MacBook can stream audio, I think this is a different issue.