DO NOT top off the fluid unless the slides and jacks are fully retracted!
You should see fluid on the dipstick attached to the cap on the fluid reservoir. If you can see it, there should be enough to fully extend the jacks.
When the motor is operating, and you hear the whine, does the whine change pitch (ie go higher or lower) when the slides or jacks stop moving. If higher, there is likely a fluid problem or something is allowing the pump motor to run without a load. I would doubt this if both slides and jacks are affected. If if the pitch is lower, something is stopping the movement but you do have hydraulic pressure.
Do you extend jacks first and level then extend the slides? That is the sequence in ours.