How do I know about the noise factor? If you recall, way back when I started this discussion, my spring helpers were completely MIA. The only thing left was the mounting plates and bolts. So I phoned Merlin right up and for $48.00/each I got two new ones. I put them on, and voila the truck was quieter going down the road. Even my wife, with out prompting, said what did you do to quiet things down. So, that's how we know. Before versus after, it's simple.