Definition of Noise

[Jae Ho Chang]

What is a good definition of noise
in terms of acoustics (or maybe mathematics)
considering not only 'white noise' but also noise in general ?

What elements in a sound make us perceive the sound as a noise?
How do we describe such elements?

The keys are
non-linearity,
non-periodicity,
unpredictability,
a continuous spectrum without any peak ?

But in many cases, non-linearity  or non-periodicity does not make the 
sound noisy, but makes the sound as what it is supposed to be. Clarinet, 
for example, makes a lot of non-linear or non-periodic fluctuation in its 
reed at startup of vibration, but if we could cut it (after recording it) 
the sound would not be perceived as a clarinet any more. Is this 
non-linear and non-periodic vibration a noise ?

In fact, I need this for my thesis,
but I think this is quite interesting to talk about, too.
I would like to hear your opinion.

Thanks.
Jae Ho Chang :>