Er, find the suit sound's name, then just place an empty .wav in your mod folder in the correct location.
IE, say the HEV suit sound is named Suit_sound.wav (just an example, not sure if it does) and is in sounds/player in the pak (or GCF for steam) file, just put an empty .wav (you can just make a file in notepad and save it as wav) in Your_mod/sounds/player/.
You don't need to remove any files or do anything, since files in folders have a higher priority than them in paks or gcfs.