Not being sarcastic but in physics terms it is called noise

W. Horsthemke has written:

'Noise-induced transitions' -- subject(s): Noise, Phase transformations (Statistical physics), Stochastic processes

'Fluctuations and Sensitivity in Nonequilibrium Systems' -- subject(s): Stochastic processes, Fluctuations (Physics), Congresses, Nonequilibrium thermodynamics

Waves of air that oscillate at a particular frequency. The ear drum picks up these waves, and then the brain interprets them.

All sources of noise are natural. Noise is otherwise defined as soundwaves, which vibrate through matter until they reach your eardrums and the energy used to cause the vibrations is translated into noise by your brain -the pitch is determined by the frequency of the vibrations-. Anyway, it does not matter how the soundwaves are created, it is all natural. You cannot create synthetic noises as far as the physics are concerned.

this has to do with physics, when it is cool in the air around de wood it makes the atoms get closer because of the cohesion force and that makes it sound..