After power steering pump is warmed up after about 30 minutes ,when I turn there is a slight rubbing sound coming from the steering column . Fluid is fine. No leaks.Any suggestions what it might be. Mechanic couldn't reproduce sound.

 

I've seem them rub on a rubber seal turned the wrong way where the I shaft passes through the floor out to the engine compartment.
if the noise is at the steering wheel, I have seen the clockspring make a rubbing noise against the steering wheel.