There are additives that may quiet it. The new fluid is likely the cause of the noise especially if an unspecified fluid was used. Many shops use an off-the-shelf fluid which may or may not meet vehicle manufacturer's specs. You can buy a GM spec fluid but, I have always had good luck in GM's with Dexron transmission fluid even though this may not be spec'd for your system. Lastly, since it gets quiet after a few minutes of warmup, it may become quieter all the time after it is driven a while. Changes in sound are common after fluid changes in power steering, transmissions or any other hydraulic system. I would give it a pass for a while to see what happens.
Lugnut