[papajam]

If I'm reading this correctly, you have a rattle in the left front that goes away when the brakes are applied. Correct?
If so, I would suspect brakepad rattle. Quite common actually on all makes a vehicles. There's a product here in the States, called disc brake anti-squeal or something like that, that is applied to the back of the brakepads. Basically what it does is lightly glue the pads to the pistons to prevent rattling and squealing.