Just bought a 96 4 door Tahoe. Excellent condition. The electric front drivers seat only makes a chattering noise when trying to move front and back. I removed the seat and hooked up 12 volts so I could operate it laying upside down on my bench. I can make it move holding the switch and turning the bar that goes across. Feels like a gear or something is loose. The gear system looks to be sealed. Is there someplace thats sells the unit? The motor that moves back and forth runs. The 2 motors that tilt and raise and lower only click when I push the buttons.

 

I'd be my guess that the gears are shot from your description

 

i could sell you seat rail or whatever you need just let me know exactly