We'll assume you pulled and cleaned the fluid filter? ;-)
Most folks probably aren't aware there is one - it's found after one removes
the large black screw lid on the reservoir. A clogged filter could
theoretically cause noise. Also, some fluids take longer to 'pop' the air
bubbles present when the system is being filled, so might be worth using it
a bit and topping up - after the filter is cleaned if it hasn't been already.

Karl
www.westyventures.com