This isn't actually a Construct 2 bug but is a stupid problem with the Safari browser. If you don't install Quicktime, Safari completely removes any audio support at all in a way which is not standards compliant, and this breaks any javascript which tries to play audio, which obviously includes Construct 2 games. If you install Quicktime, it works.
Maybe I can add a special alert for Safari for Windows. But it's really not a very good browser for Windows (it's much better on Mac) and I don't think many people use it, so I don't suppose it's important other than to stop scaring people who are testing their games on as many browsers as they can find.