All of our SVTF's rattle. Mine does it in the winter but not really at all in the summer, so I've learned to live with it.
2004 Silver WRX 300+whp
2003 BMP VW Golf GTI 20th AE #2845/4000
2002 Sonic Blue SVT Focus #1200/4788
2000 T-Red SVT Contour #1089/2150
1998 BDP Subaru Impreza 2.5RS #1595/1695