Gearbox "clicking"

Hi - I'm a newbie (ex Honda owner) - thought I'd venture in the world of VAG and buy a Octavia TDI (2011).  I went for the 1.6 as it seemed to have a decent balance of power & economy.  I'm no street racer !

Whilst it might seem a minor thing, one issue I've had is that the gearbox "clicks" loudly, especially when shifting "down", ie into 2nd or into 4th. This spoils an otherwise quiet and smooth driving experience. 

At first I thought it was loose trim, but it isn't.  It's definitely "upper", ie not the gears themselves ?

What could this be ?  Any suggestions or similar experiences most welcome.