Probably the most replaced audio file is...
Objective_loop.ogg
This is the glowie sound. I wanted to make this thread to ask what you're replacing it with? There are lots of options already available in the CoH Modder by The Philotic Knight.
I recently found this on youtube, so I'm trying it as my glowie sound, but I don't want to upload it because of ©opywrong.
So.. what are you using?