Actually I had a similar problem I posted about it a while back, my power steering fluid was full (I thought) as well.
Is the sound only around turns? I was told I needed a new steering rack or suspension. Friend of mine in VA said he wanted to try something, poured some steering fluid in and it fixed the problem, hasnt come back since, he said that it will read full when sitting still, even if its not all the way full, then around turns it becomes more shallow on one side or the other causing the sound you hear going around turns. If you only hear it around a turn and then for a few minutes after you probably have the same issue I had.
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Modified 2001 Grand Prix GT 3800 Red/Orange Kills: Acura RSX type-S, Early 90's Rx-7, Mustang 5.0GT, Modded Cavalier, Assorted Civics, Assorted Integras, Sentra SE-R Spec-V, F-150, Early Modded Golf, Modded GP SE, Stock GP GT, Altima 2.5S, Maxima. Killed By: Modded RSX-S, Heavily Modded Older RX-7, 2005 Altima 3.5, VW Bora Modded, Modded Turbo'd Jetta. Now retired till further modification.