On a previous 5'er I owned, the slides rubber seals became sticky ( after a long period of non-use) and would not let the slide move out. I used the manual crank as others suggested to get the slide out, lubricated the slide seals with a factory recommended lubricant / conditioner and all was fine. The ratcheting sound is likely due to the clutch mechanism sensing too much resistance. This can be caused by sticky seals, an obstruction, mechanical problem with the slide rails (rust/ corrosion).
Another possibility is poor or inadequate power to the slide motor. If your battery(s) is even slightly down, you will not have enough power to overcome the slide resistance and the clutch will engage.