There is a steel "drive gear" with two plastic rollers on each ram. They are mounted on the outside of the frame rail, where the ram goes through the frame. The plastic rollers tend to wear and if you've hit any significant rough spots while towing, one or more of the plastic rollers may be broken. I had two broken and one flat roller on my main slide last year.
The gear "rack" shown on the bottom of your rams in the photo you posted are "driven/timed" by the gear/roller assembly. Follow those teeth on the bottom of your rams and they will lead you directly to the assemblies in this link.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
You can buy new roller assemblies for about $50 each. There are two gear drives, one is 15 teeth and one has 18 teeth. I can't tell you what year Keystone used which "tooth count gears"... You'll need to count the teeth on your slide mechanism to know for sure. The replacements come with 15 tooth gears, so if yours are 18 teeth, you may need to switch the gear wheels so they mesh properly.
I would inspect the gears and especially the rollers very carefully. You may be lucky without damage, but the same "noisy slide movement was my first indication that I needed to replace broken parts.