GS300Tex

Hi, I'm new to the Lexus forum. I have a 2003 GS300 w/120k miles. She's been a very good car to me over the last 4 years. I recently noticed a whiney noise coming from under the hood. It doesnt make the noise when turning the wheel, only when the car is still or driving in a straight line. I checked the power steering fluid, it was a smidge low, so i added a little, but still didnt help. Any input you have is GREATLY appreciated :) Thanks! GS300Tex