Whiney Power Steering

Greetings all:

My Tacoma is an '03 PreRunner, 2.7/automatic. Some time back it developed that power steering whine/growl like low fluid, but fluid wasn't the issue. I had the pump rebuilt but the issue continued.

It goes like this: Start the truck cold and it sounds fine, but when it's up to normal op temp, it starts growling. The rebuilder promised me the pump was fine. Since I had no leaks, his solution was to replace the return line, with the logic that air in the system was bleeding itself out at night but was being sucked in during operation. I replaced the return line. Issue remains.

Anyone else dealt with this? And have a remedy?

Thank you!