Just to add another data point, we're testing out these Arkel Dry-Lite panniers. Like other Arkel products, the bottom is secured with a hook connected to a piece of bungee cord. But instead of hooks that clip to the top rail of a rack, they sit more like saddlebags with adjustable straps that reach over the top of the rack.




Here's a photo from their website of the straps that connect the two bags and sit on top of the rack.



It's a super simple system and since there are no clips or hooks or mechanisms to attach to the top rail of the rack, there's no rattling. We rode some trails with fist-sized rocks last weekend and the bags didn't budge.