If it's a freeware program you're making, is it really to hard to attribute the sounds you use? Seriously, what's the big deal?
you can do whatever you want to them. but you still should make note of who's sample you took and tweeked to begin with. after all YOU STILL ARE using someone else's work as a starting point.
well hopefully now your question is answered.
Whatever you change them or not these sound are protected by the cc license,
so YES you can change/modify/destroy them,
BUT these sound must be credited to their ORIGINAL author/freesounders...
...and I will repeat:
you must credit the soundS used here,
you must credit the soundS used here
you must credit the soundS used here... :lol: