A decoupler for an endless drive arrangement which includes a crankshaft-driven pulley, an alternator pulley (24, 124) mounted to an input shaft of an alternator has a regulator which operates at at least first and second switching frequencies, and an endless drive member that is positioned to transfer power from the crankshaft pulley to the alternator pulley (24, 124), wherein first order vibrations are produced at the crankshaft, the decoupler comprising: a hub (22, 122) that is mountable to the alternator shaft such that the alternator shaft co-rotates with the hub about a rotational axis; a pulley (24, 124) rotatably coupled to the hub (22, 122), the pulley (24, 124) having an outer periphery that is adapted to engage the endless power transmitting element; an isolation spring (28, 128) positioned to transfer rotational force from the pulley (24, 124) to the hub (22, 122) and to accommodate torsional vibration between the pulley (24, 124) and the hub (22, 122); characterized in that, the decoupler is further comprising: a first friction surface (60, 160) operatively connected with the pulley (24, 124); a second friction surface (62, 162) operatively connected with the hub (22, 122); a biasing member positioned to exert a bias force between the first and second friction surfaces (60, 160; 62, 162); and a retainer engaging the biasing member to maintain the bias force, wherein the second switching frequency is near a natural resonance frequency of the decoupler and the bias force between the first and second friction surfaces generates a damping torque during relative rotational movement between the pulley (24, 124) and the hub (22, 122) which attenuates said first order vibrations so as to reduce a tendency of the regulator of the alternator to operate at the second switching frequency, thereby reducing a tendency of the alternator of transmitting vibration to the decoupler at frequencies near the natural frequency. a hub (22, 122) that is mountable to the alternator shaft such that the alternator shaft co-rotates with the hub about a rotational axis; a pulley (24, 124) rotatably coupled to the hub (22, 122), the pulley (24, 124) having an outer periphery that is adapted to engage the endless power transmitting element; an isolation spring (28, 128) positioned to transfer rotational force from the pulley (24, 124) to the hub (22, 122) and to accommodate torsional vibration between the pulley (24, 124) and the hub (22, 122); characterized in that, the decoupler is further comprising: a first friction surface (60, 160) operatively connected with the pulley (24, 124); a second friction surface (62, 162) operatively connected with the hub (22, 122); a biasing member positioned to exert a bias force between the first and second friction surfaces (60, 160; 62, 162); and a retainer engaging the biasing member to maintain the bias force, a first friction surface (60, 160) operatively connected with the pulley (24, 124); a second friction surface (62, 162) operatively connected with the hub (22, 122); a biasing member positioned to exert a bias force between the first and second friction surfaces (60, 160; 62, 162); and a retainer engaging the biasing member to maintain the bias force, wherein the second switching frequency is near a natural resonance frequency of the decoupler and the bias force between the first and second friction surfaces generates a damping torque during relative rotational movement between the pulley (24, 124) and the hub (22, 122) which attenuates said first order vibrations so as to reduce a tendency of the regulator of the alternator to operate at the second switching frequency, thereby reducing a tendency of the alternator of transmitting vibration to the decoupler at frequencies near the natural frequency.