Yes I think it can ... I havn't tested or worried about it myself tho BUT heres what you can do

in the FS9/Captainsim/c130/sound folder theres the following sounds

clear.conflict
climb
descent
tcas.fail
tcas.ok
traffic

open those sound files in a sound editing program, like goldwave, which you can use for free at goldwave.com (i hope im not violating the rules by posting this)  open each sound in goldwave, click effects, and find volume: and just change the volume level, and hit save

should work, but just incase backup the files