Celica 2003 Air con rattle.

[Grahamr123]

I've recently bought a T sport Celica 2003. All is great except the Air Con. It works fine, gets the cabin cool pretty quickly. Problem is that outside the car it makes a rattle sound.

Its overdue a service anyway, so I'm getting one done next week. However I don't know what it could be and If I should expect any large repair bills coming my way for it.

Anyone have any idea what it could be?