Hi matts5150, :xoutpost:

Most likely the sunroof. What year model do you have? This was a common problem on 2004 and early 2005 models.

Also, try running a search for water leaks, sunroof leak, etc.

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'05 X3 3.0i Alpine White/Gray Leather/Alum. Trim
Sport/Steptronic/Servotronic/Panoramic
Prem. Sound/Staggered 18" Style 114 Y-Spokes