Does it only when I first start it and turn the wheel as I back out of the driveway. Once it warms up the noise goes away. Fluid is topped off, but it's the original fluid with 122K miles. Can old fluid do this or is the pump going out?

 

Most older Ford ps pumps are going. Mine sounds like this...WeerrrrrrrrrrrRRRrrrrrrrr........weeerrrrrr rRRRRRRrrrrrrrr. Pretty good huh?
Chattering sounds kinda unusual for ford. Check to see if anything is loose. Look for leaks. Have someone move the wheel when its cold while you take a look.