Low power steering fluid noise

My 2005 Honda Odyssey has started making the noise I associate with low power steering fluid when getting off the freeway after a long trip. When I check the reservoir it is full. What else could be causing this? Is it a matter of a bubble in the line or something?

The pump may be starving for fluid, caused by a plugged filter screen hidden down inside the reservoir. Hose particles can plug this screen, making the pump moan…You can empty the reservoir with a turkey baster…