Air is present in the fluid.

Inspect and bleed the system. Refer to Power Steering System Bleeding .

The fluid is low due to improper initial filling or a system leak.

Inspect and bleed system. Refer to Checking and Adding Power Steering Fluid .

The pump mounting is loose.

Torque the pump mounting to proper specifications. Refer to Power Steering Pump Replacement .

The power steering gear inlet (pressure) hose is grounding out.

Check and adjust for proper mounting and clearance. Refer to Power Steering Pressure Pipe/Hose Replacement .