The pressure plate is not flat against the cam ring.

Replace the power steering pump. Refer to Power Steering Pump Replacement

The cam ring is extremely worn.

Replace the power steering pump. Refer to Power Steering Pump Replacement

The pressure plate, thrust plate, or rotor is scored.

Replace the power steering pump. Refer to Power Steering Pump Replacement

The vanes are sticking in the rotor slots.

Replace the power steering pump. Refer to Power Steering Pump Replacement

The vanes are not installed properly.

Replace the power steering pump. Refer to Power Steering Pump Replacement

There is air in the power steering fluid.

1. Locate and repair the leak. Refer to External Leakage Check .
2. Bleed the power steering system. Refer to Power Steering System Bleeding .

The power steering fluid level is low.

Check and add power steering fluid, if necessary. Refer to Checking and Adding Power Steering Fluid .

The pump belt is slipping.

Inspect the drive belt for wear. Refer to Drive Belt Replacement in Engine Mechanical.