Been having this issue lately. When backing the car out of the garage and transitioning the car from reverse to drive, if I attempt to turn the steering wheel before the throttle is applied, the steering wheel vibrates horribly and the steering pump groans. Only does it at low RPM's.
Things I've checked:

1. Steering fluid - Full
2. Belt is tight with no obvious cracking
3. No suspension damage

What else could it be? Pump going south?

TIA

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2006 4.8iS Black/Black with custom Audison Voce/Image Dynamics sound
Production Date - 10/05