A multi-ribbed power transmission belt has transverse grooves in the compression section which are oriented at angles other than perpendicular. The combination of longitudinal grooves and transverse grooves form a plurality of cogs on the belt surface, with a row of cogs being defined between adjacent transverse grooves. Each cog has a pitch length P extending from a location on the cog to the identical location on the longitudinally adjacent cog. The pitch lengths of the rows of cogs are randomized over the entire length of the belt to reduce the noise of the belt as it travels about its associated pulleys.