The last part of the safety valve - the part that is bolted to the boiler - is best left in place, just because a special wrench is pretty much needed for installation. (Stefano has the wrench for sale, and some socket wrenches work.)

What can happen is scale builds up right where the ball bearing makes contact. In early stages of buildup a whack can free things up. This is much more of an issue with modified 'Ultimate' Europiccolas that have a vacuum breaker from later models retro-fitted into that space. (This mod is not applicable to minimo/maximo configurations.)

If you want to get an idea of what the venting noise should sound like, here's a video from Prima Coffee done by Steve, a member here: