noisy tow hitch

on my way home from stover last weekend my hitch started sqeaking loud enough for me to hear it in the car. when i got home i had a good look at the alko pads which seem fine but a little sooty for want of a better word, would this cause the noise or could it be somthing else, also what best to clean the pads with? normally i just wipe the inside with a cloth before i hook up