Hissing noise from power steering pump

I have a 99 durango with 5.9L motor, I have owned it for a couple years and ever since I owned it when turning the steering wheel you hear a hissing noise from the power steering pump is this normal for the Durango? or is the power steering pump bad? Anyone else have the same problem?

Thanks

I have a 99 D with a 5.2 and have the same noise, I think it's just a normal noise, I don't have any problems with the steering other than the noise and thats only when the Durango is sitting still