Detached air pipe (?) in engine
 

Sorry for topic heading, I'm not a mechanic so I'm sure my naming is wrong. My car is a T5 and I'm having a problem with what I think is a loose air pipe.
In the engine compartment, just behind the radiator, there is a wide grey pipe which comes off the back of the radiator and disappears into another big box thing on the right - how am I doing on the technical stuff :) It's the air intake for the intercooler I believe.
The pipe where it connects to the back of the radiator has come loose twice now. It looks like it just clips back on, my garage has clipped it on once and I've just done it again myself.
When the pipe comes off there is a lot of extra wind noise. But, even after clipping it back on the last time it's much noisier than it should be. The noise is best described as a flapping sound. Also, the rest of the system (the big box) rocks quite a bit on it's mount. Is this normal; it doesn't feel like it's going to come off and the garage thought it was OK.
Any ideas, is this a known weakness or problem?
The noise only appears at high speed (read illegal in the UK) which I've always found garages use as an excuse for not being able to reproduce it.