Couple of things to look for. Prior to replacing the belt I would have checked all the pulleys not only for bearing issues but also for debris. Possible an acorn or a rock could find stuck in the vee pulley. Next would be the pivot point on the idler arm. Make sure it moves freely and greased. Third if all those check out fine I would look at the idler spring. Sometimes if it is weakened from age it will pulsate with the demands of the hydro pumps. Taking a guess on the idler because I don't know your model and serial number. Pulley 781856, idler spring 781443.