Check idler pulley
WARNING: This page is about a different car, the 2004 Volvo S40, 2003 Volvo S40, 2002 Volvo S40, 2001 Volvo S40, and 2000 Volvo S40. However, it is still accessible from the selected car via links, so may be relevant.
Courtesy of VOLVO CARS OF NORTH AMERICA.
Rotate the pulley rapidly and listen for abnormal noise from the bearing.
When replacing: torque setting idler pulley 25 Nm
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Check that all pulley contact surfaces for the belt are clean and smooth.