I also had a rattle in my 04XC70 that was driving me nuts. I was a rattle that was similar to what you might expect to hear from the dash speaker grill. I finally discovered that it was the small plastic document holder that is mounted inside the windshied on the drivers side. It still tries to rattle occasionally and I just push on it to shift it's position slightly and the rattle disappears. I can get pretty loud and annoying.
2004 XC70 - Ash Gold/Taupe, Premium, Touring, Integrated Boosters, rear skid plate.
2004 S60 - Ash Gold/Sand, Premium, Touring.
John Deere GX-345 (main ride) Green/Yellow
"To Have Peace, Teach Peace"