Y is the carpet in my x5 boot wet (where the sat nav goes)

Most likely the sunroof casette is leaking; either the drains are clogged,the casette is allowing water to leak, or you have the older casette with poor water management;i would open your rear hatch and check the drain, with the hatch open, there are two drains one on each side at the top of the body, where the hatch meets the body; there is a small door to each drain(recommend removing) if you open that small door and water pours out most likely thats the souce of your leak. you can also see if you can push water into the drains to unclog them; you can also lower the headliner in the rear, open the sunroof, and pour water into the casette to see where the water leaks out and go from there; usually the backing on the headliner doesn't soak up water and it channels the water into one area; since your vehicle is an 05 and hopefully under 75000 miles the dealership can goodwill a repair. you may even look into an aftermarket extended warranty and make sure they cover the sunrrof in the warranty; replacing a sunroof casette is a big job, not recommended for the diy;