Air is present in the fluid.

Inspect and bleed the system.

Refer to Power Steering System Bleeding .

Fluid is low due to improper initial fill or system leak.

Inspect and fill the system.

Refer to Power Steering Gear and Pump Leaks and Checking and Adding Power Steering Fluid .

The power steering pump mounting bolts are loose.

Torque the power steering pump mounting bolts to the proper specifications.

Refer to Power Steering Pump Replacement .

The power steering gear inlet (pressure) hose is touching other parts of the vehicle.

Check and adjust for proper mounting and clearance.

Refer to Power Steering Pressure Pipe/Hose Replacement