SteeringColumn Noises 2002 Prius

I am hearing a squeaky sound emanating from the steering column of my 2002 Toyota Prius when I turn the wheel to the left. It sounds like two solid things rubbing against each other. The peculiar thing is that the sound doesn't start happening until about 20 minutes after I've been driving the vehicle, and it doesn't happen when I turn the wheel to the right (just the left).
I took the car into a high rated local mechanic and they replaced a Steering Shaft U-Joint, which they said was failing. However this work did not stop the noise. I notified the mechanic that the noise is still happening, and they said that they assured me that the vehicle is safe, and that the noise is just an inconvenience, not a mechanical problem. The noise can sound pretty bad at times, and I'm considering taking it in to the dealer.
Any thoughts on what the problem is or what I should do? I no longer live in the same state as the mechanic, so taking it back to them is not an option. The vehicle has only 67k miles on it and has been maintained very well in its lifetime.

Are you absolutely certain the noise is coming from the steering column inside the car and is not from under the hood and just telescoping through the column? Have you tried opening the windows and turning left when between a couple of buildings, or while someone is standing outside the car, to confirm the noise is only inside the cabin?

-Rod