Moved to "General Technical Chat". I would suggest changing the power steering fluid first to see if that alleviates the problem. If that doesn't help, I would first have the pump checked to see if it is still working properly. If it's not any of those problems, then check the rack.

 

Several ways it can happen.

Blown rack piston seal.

Trash suddenly stuck in pump bypass to block it open and no pressure then. Dirty fluid.

There can be a couple of ways the torsion valve in rack can fault to internal crossleak. Valve can even break.

Air in system moans or whines, no other way about it, you would hear that. If the pumping section of pump is damaged you should be able to hear that as well.

May be nothing wrong with pump at all. 50/50 chance.

Long shot here.................I've seen an oddball situation where a belt slightly too short and belt tensioner broke but belt did not come off since still almost tight. The car seemed to still run right, only thing wrong was that power steering was acting up like none there. Reached down and pushed down on belt between pump and motor mount, the belt was too loose to work right. Change tensioner (spring broke in it) and car went back to running fine with full PS.

 

It has been quite a while but I figured I would update since the problem has been solved.

Before replacing the pump, I decided to change the fluid first to rule out a variable. As it turns out, the fluid was the culprit. With fresh fluid, it has worked flawlessly for the past eight months.

So now I have a spare OEM power steering pump in case I ever need it in the future.