Vibrators are constructed in many different ways, but most frequently, a vibrator vibrates due to a rapidly rotating motor with a heavy weight or bearing. The off-balanced weight spinning around in there so quickly is what makes the toy vibrate. Suction toys, on the other hand, typically operate one of two ways. One way involves a chamber pressed against the body that has the air sucked out via a small hole, creating low air pressure inside the chamber and suction against the body. This is the same type of pressure created with penis pumps. The other type of suction toy is created by having a chamber pressed against the body, but instead of a hole to pull the air out, there is a thin membrane that gets pushed in and out rapidly, causing alternating high-pressure and low-pressure in the chamber, sort of like a sucking mouth.
Depending on the models of the toys, the sensation of the rapid suction and vibration can feel a little similar. However, some have both a vibrating motor AND a suction chamber – such as clit sucking vibrators – that are both targeting external areas. Additionally, there are dual-stim toys with internal vibrating arms with external suction.