Which type of vibration can be described as random and might result from external impacts?

The type of vibration characterized as random and potentially resulting from external impacts is indeed noise or a raised noise floor. This type of vibration does not follow a predictable pattern and is often created by various unpredictable factors in the environment. These could include machinery operating, collisions, or environmental disturbances, all of which introduce random fluctuations into the vibration profile.

Noise in vibration analysis refers to components that can obscure or interfere with the more structured, periodic signals associated with machinery operation or system behavior. The presence of noise can complicate diagnostics and analysis, as it makes it difficult to distinguish between meaningful signals and random disturbances.

In contrast, harmonics represent specific frequencies that are integer multiples of a fundamental frequency and indicate a structured form of vibration. Sidebands are variations that occur around a fundamental frequency due to modulation or disturbances, but they are also more predictable than noise. Static, while a form of vibration, does not involve motion or dynamic variability at all, which sets it apart from noise that signifies random events affecting the vibration spectrum.