It might not the be same sound, but in mine I get a loud Clack or Click noise when I change gears (can only hear it in the lower changes, where significant masses are exchanged and the engine noise isn't so loud), and also when I am in reverse and play around with the clutch catch point. My mech said it's a ball-headed bolt that sits between two thick wires on the same arm thing as the throw-out bearing.
The thing that makes your problem sound familiar is that some said it happens on gear changes and/or when there is load on the drivetrain, that's exactly when mine occurs (e.g. a clumsy change will also show it up fairly obviously).
But the sound I hear is most definitely from the gearbox/clutch area, so like I said, might not be the same. My clutch is getting changed out on Tuesday, so I'll try to get a recording of the sound before then.
Suggestions for where it can be uploaded? (if anyone is interested...)