I think most of the "rattling ROPS" comes from ones that were assembled incorrectly. Mine has a set of washers on the inside between the folding member and the stationary member. The bolts that it pivots on are castleated, and are relatively snug. To fold up/down takes a fair amount of force (i.e. it won't fall when bent in a 45 degree angle. I would estimate that it takes at least 15 pounds of force to move it.
The GlueGuy