This will not immediately seem relevant.
I finished watching a "Gnomon Workshop" DVD on using fluid effects to generate explosion effects in Maya. The basic concepts was that you place effects emittors and manipulate "functions" at various time indexes. For example you could manipulate the Y position of the effects such that it rises, modify the turbulance effects such that it creates swirls of smoke that roll over each other, manipulate colors such that initially, when the explosion has a lot of heat, the explosion appears a bright yellow and over time moves into reds and then blacks as it cools down. Throughout the process the concept is that you modify settings at various times in order to produce the flow of graphics. This influences how I perceive the crafting of sounds.
I've fiddled a little in Audacity, made 3 "plucks" (plucking a guitar string), overlapped them, applied effects at various time ranges and ended up with a nice effects (the first I ever made, so it was nice to me but would have been awful to a professional). There's a myriad of effect plug-ins available, and new ones can be programmed in the Nyquist language.
My first attempt jumbled everything on top of the other, making it impossible to go to a time range and edit the parameters of the effect I applied. Maybe the solution is to apply the effect to different tracks and Audacity would merge all the tracks.
There's a list of sound/audio editors on sourceforge.net: http://sourceforge.net/softwaremap/trove_list.php?form_cat=120&discrim=219
. That list has been limited to Windows software but if you remove the &discrim=219 at the end of the line you'll have access to Linux software as well.