out door carpet perhaps, example what is placed on trailers for boats.
not sure if you could get any sort of paint on or spray on rubber up into the rail areas. to help create a cushion. the rubber may end up not allowing things to slide easily. though they do have different pond liner rubber materials abs / pvc that might be a bit more slicker vs going with a EPDM thicker rubber.
grease the snot out of the rails. so entire ramps moves vs catching up rust and like and then suddenly forcefully coming flying and hitting something causing extra noise.
if there is extra space, might say a nylon strips (hard plastic) you still maintain your slickness to make it easy to pull/push ramps in/out. but you loose direct metal to metal rattling. i say nylon due to it is a tad softer and will grove up some from wear and tear (bouncing of the ramps around). but more likely not crack and shatter like a hard plastic.
just a straight C clamps were clamps ends are metal most likely not going to do much. find some "rubber" ends say 1/2" thick, then what ever additional rubber is needed to attach to clamp. the rubber more likely help absorb movement and let things adjust/slide/move just a bit, but not allow full slop of ramps just rattling and rolling.
post some pictures of the rails in trailer, and then ramps pulled out, then ramps pushed in. it might give others including myself better idea of what you are directly dealing with.