Well I waited to get in this one. I don't own a designer trailer but I have had "squeak" problems with others. It turned out to be the spring sets themselves. As they move and bounce the leaves shift together. Even little movements will shift them together. They will squeak if they are dried out or the touching surfaces have rusted a little. To lube them, lift the trailer weight off them to separate the individual leaves and spray some heavy grease in between them. Also lube inside the shackle bushings and hangers too. See if that helps. If the squeak doesn't go away at least having lubed the leaves wont hurt them.
I also had to do that to a Chevy truck I towed with. The spring clips that kept the leaves tight had loosened and come off. That allowed the individual leaves in the spring set to move.
Frank
