hmmm...on the rattle or knock sound, honestly, i think everyone would agree that you kind of need to be there to hear and see it to diagnose it. with regards to the hydraulic fluid, if your just topping off i can't see why "regular" 10w30 conventional motor oil wouldn't be fine. actually if your draining and changing the hydraulic oil, i've used regular Napa conventional 10w30 oil, and with my amazement the hydraulics worked! ha! yeah it'll be fine, i just don't like mixing different types of oil, if thats the case i'd drain and begin with fresh stuff