Received crossbars for 2016 GT, read instructions and ready to install. My question is about instruction #2. The rear crossbar stanchion seems very loose, ( a lot of slide movement) vs the front crossbar. My concern is the crossbar going to rattle? Should I size the rack onto the rails then tighten the stanchion? It just seems very loose. I realize once I attach, the movement shouldn’t be an issue, I’m just concerned about rattling noise.