A few common parts are found in all switches. There is the physical switch itself, which might be a metal bar lever, a circular plunger, or a plastic tab. Then there is the locking mechanism found in push-on push-off type switches. To make electrical contact a switch has its "poles" and "throw" which are the little metal contacts which move into position. Finally there is the resonance of the switch housing or the panel on which the switch is mounted. When a switch is activated a throw arm moves across pushing the metal contacts into place, but to keep a good electrical connection the contact is usually made of some springy material like phosphor-bronze which bounces briefly against the pole. This is where the requirement for switch "debouncing" comes from in electronic circuits. Although the bounce is tiny, perhaps less than 2ms the ear can pick it up as a metalic ringing sound.
Let's start with a crude but efficient model of the above description. We have created a filtered noise source to get us three tones which sound like a small metalic material. Actually I have chosen values somewhere between a metal and plastic noise to save on atoms. Sequencing these to appear just a few milliseconds apart creates a nice clicking sound.
While it makes a nice single click the sound lacks complexity that might convince us it's a switch. Taking the lazy way out we just duplicate the parts and change some of their parameters, this time to get a more plastic sound. Tweaking the volume and delaying the new part by a few milliseconds gets us a better sound. The delays are chosen so that the plastic sound happens first, then again with the metal click on top of it shifted by five or ten milliseconds, which roughly corresponds to the way a panel switch works.
On its own the switch sounds a bit too bright and neutral so I've added some resonance to it now. Using a short delay with a little feedback through a low pass filter gets us a sound more like a switch attached to some piece of equipment. By changing the delay times, feedback values and filter characteristics it's possible to get the switch to sound different, as if it was mounted on a large metal plate, or on a small plastic box.
