I agree with splashing. Just a few drops of water between the top edge of the glass and the lid will cause it. Capillary action will cause the water to fill in the gap. Once the water evaporates/drys, the salt content will remain behind and grow in size as it drys out. My Evo was doing the same thing when I had the stock lid. When I removed the lid, it stopped. When I put a screen top on it, I had salt creep again.
Try aiming the output of your power heads/ wave makers just a little lower and experiment with the water level in your tank, if coral placement allows. I dropped my water level only about 3/16” and I stopped getting creep around the rim.
Hope this helps!
Mike