The Lippert electric slide operator has a slip clutch in the motor. Due to it's design, when the motor overloads and the clutch slips, it will make a clicking sound. If this is your symptom, check for binding or obstructions to the slide's free movement.
Some systems have a crank for manually operating a slide, others may have a release lever located in the mechanism and a shaft to turn with a wrench. Make sure your batteries are up good, slides run off of the battery's power and not from the converter.
'11 GMC Acadia SLT AWD
'11 GMC Sierra 1500 4x4 Extended Cab