What causes some gas diffusion to be noisy, others to be quiet? My question is about noise in gas diffusion, specifically when a can of pressurized gas is opened into the atmosphere. I want to know why this is noisy sometimes, but quiet other times.
Does the gas composition matter? I used to think only the pressure and size/shape of the hole mattered, but is it actually the gas that makes the noise, or the vibration of the solid can that releases it?
Edit: The question came from curiosity in my own experiences. Hand pumping air into car tires, for example, produces a little hiss despite dealing with 30 to 40 psi. An aerosol can, however, produces a lot of hiss but I'm pretty sure the psi is less.
 A: The sound could be turbulence, which would depend on the flow velocity, density, and viscosity of the fluid, or on vibrations in the solid aperture, which would be excited by the fluid dragging on the edges of the opening. So fluid flow, density, and viscosity would be relevant, but also the spring constant and mass of the solid parts. Flow rate would of course be a function of pressure, among other things. 
A: I see this is an older question, but it's still worth an answer. 
Sir James Lighthill did much to advance the understanding of sound generation by turbulent jets. In his 1961 paper (pg. 169), he suggests that the amount of sound energy radiated by a turbulent jet in the absence of convection effects is related to: 


*

*density of the undisturbed medium, $\rho_0$

*the speed of sound in the undisturbed medium, $c_0$

*the mean velocity of the turbulent jet, $U$

*the diameter of the jet, $d$


Such that:
$$P = K \frac{\rho_0 \ U^8 d^2}{{c_0}^5}$$

Lighthill mentions that the power estimate is actually per unit volume, and since volume of the jet increases with distance from the nozzle, $x$, he flags that as a concern. Helpfully, though, he puts a spatial bound on where the above estimate should hold:

"The sound emitted per unit length of jet should remain constant... ...up to $x = 4d$"

 Finally, he goes on to describe some good experimental evidence for the relation, where the proportionality constant, $K$, is:

"about $3 \times 10^{-5}$ for jets emerging from a nozzle with low turbulence level, $6 \times 10^{-5}$ for jets emerging from straight pipes and as much as $10^{-4}$ for jets with a very high level of initial turbulence."

His research was on jet engines, though, so I'm not sure how these hold for aerosol canisters!
