There are two plastic "covers" that run front to back on each side. Many people have reported them being a little loose after hearing a noise and tracking it down. I did not hear a noise but I did find them both loose.
They have regular nuts holding them in a couple of places, those were tight on mine but others found some of them loose. BUT there are several plastic nuts that need to be hand tightened and all mine were loose one or two very loose. I believe they can not fall off/be simply screwed off but they do need to be hand tightened.
I would check there?