What is that mysterious ticking noise? Can anyone help?

Hi ever since I bought my Mk4 Golf it has had a ticking noise coming from the engine bay only after the car has warmed up, the garage I bought it from said they looked into it but couldn't fix it because they didn't know were the noise was coming from, anyway I was checking the filters today in the engine bay, went to start the car up (I had previously driven the car about an hour before) and of course the ticking noise was their but because I had the bonnet up I could hear it a lot more, normally its very hard to hear if not unnoticeable from inside the cabin anyways does anyone know why its ticking. I managed to get a shot of were the ticking is coming Its the black box just above the washer bottle, I have no idea why its ticking or how to stop it (Don't really want to go to VW and pay their prices for nothing!) Any advice or personal experience with this sorta thing is much appreciated,

Thanks in advance.