A decoupler for an endless drive arrangement which includes a crankshaft-driven pulley, an alternator pulley 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 , wherein first order vibrations are produced at the crankshaft , the decoupler comprising: a hub that is mountable to the alternator shaft such that the alternator shaft co-rotates with the hub about a rotational axis; a pulley rotatably coupled to the hub , the pulley having an outer periphery that is adapted to engage the endless power transmitting element ; an isolation spring positioned to transfer rotational force from the pulley to the hub and to accommodate torsional vibration between the pulley and the hub ; characterized in that , the decoupler is further comprising: a first friction surface operatively connected with the pulley ; a second friction surface operatively connected with the hub ; 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 and the hub 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 that is mountable to the alternator shaft such that the alternator shaft co-rotates with the hub about a rotational axis; a pulley rotatably coupled to the hub , the pulley having an outer periphery that is adapted to engage the endless power transmitting element ; an isolation spring positioned to transfer rotational force from the pulley to the hub and to accommodate torsional vibration between the pulley and the hub ; characterized in that , the decoupler is further comprising: a first friction surface operatively connected with the pulley ; a second friction surface operatively connected with the hub ; 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 operatively connected with the pulley ; a second friction surface operatively connected with the hub ; 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 and the hub 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. <EOS>