WARNING: This page is about a different car, the 2002 Volvo C70, 2001 Volvo C70, 2000 Volvo C70, 1999 Volvo C70, and 1998 Volvo C70. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Identifying Parcel Shelf Gaskets And Loudspeakers
Courtesy of VOLVO CARS OF NORTH AMERICA.
Ensure that the gaskets on the underside of the parcel shelf are intact and in contact with the loudspeakers. Damaged gaskets must be replaced.