power steering hissing

[lilbrudder]

ok guys, who knows what's up? i have a hissing noise for about 10 seconds after start up and every time i tap the gas after that. i've isolated this hissing noise to the power steering pump/resivoir area so i figured o-ring, but that did not fix it. i'm not losing any fluid and the level seems good. next replaced both belts and tensioner bearings, still no relief. i'm not sure how to tell if the pump is bad, any ideas? also the pump pulley seemed to spin smooth by hand, with no play. i'm going to add more fluid to see if that might help. should i try the o-ring again? i don't have bubbles in the tank does that mean o-ring is good? please give me your 2 cents, cause i'm out of ideas. thanks.