Original post by: sm_vulkus ,
It could be the actual belt that drives the pump. Or a seized idler pulley. Pumps themselves do not usually makes that noise, unless the bearing in the pump is shot. Lift the bonnet/hood while engine running and in park/neutral with handbrake/park brake on. Then watch the pump pulley as it spins, have an assistant turn the wheels slightly side to side. With engine off, twist the pulley belt sideways to check flex and slack. If you can turn the belt 180 it is time for a new one. Also check the pulleys and idler pulleys with engine off by just grasping them and trying to wiggle them by rocking them back and forth in a top to bottom position. Your're checking if they will move forward and backward in either a 12/6 or 9/3 position. They should be tight in that regard.