They're just normal springs wrapped with a coating which started peeling off immediately after mounting them.
They're not noiseless at all. They have a specific resonating frequency which, when played, makes them resonate like crazy. With my setup it's somewhere around E flat.
Also they are way stiffer than the other springs. My old setup had 3 springs with the claw quite near to the body. With these I only put 2 springs in, with the claw quite far from the body. This makes the floyd really stiff and uncomfortable when diving. On the good side it improves tuning stability.
Others have mentioned they create electrical humming issues because they interrupt the grounding circuit of the guitar (the coating doesn't conduct electricity), but I didn't check that out because I uninstalled them before I even plugged my guitar into my setup.
So in my case I just reverted to my old setup: normal springs with bands of narrow Velcro tape wrapped around them, and they work perfectly.