uplock actuator

[RandyArizona]

Hi Burt,
Best guess: Your hoses or fittings have a crack / leak / loose. The "squeel"
You hear is air coming out, or being sucked in. (The mule... does it have any way to check if the fluid is frothy, ??)
It only "squeels" when under pressure, so the manual pumping is not enough pressure to "suck the air".
Check fittings, if hoses are older than about 8 years old, replace.
(Also check for wetness around the fittings, under hose sheath. DO NOT STICK YOUR HAND UP THERE WHEN UNDER PRESSURE!! You could lose a finger, or two.)
Good luck.