Recently on my '97 Ranger, 4-cyl., after it has been running for at least a half hour, I'm getting a low whining sound when I turn the wheels. Could this possibly be the power steering pump, or maybe a bearing? It doesn't affect the performance at all. I changed the serpentine belt three weeks ago, but no change. Get worse after it's warmed up. Whatcha think?

Guessing you already check the fuild level, then it just might be the pump.