There is no such thing as two sounds at once. You have one sound that you interpret correctly as two things. Noise reduction is a finicky thing, and more often than not, only useful at removing consisten noise(white noise, hum, ambient noise).
Actual sounds have too much character to be interpreted correctly by a noise filter.

What is your intended use for the sound in question?

I want to use the sounds for a gunshot in a mod. Me and a few mates are wanting to get some modding experience so we're just doing a WWII mod for HL2, so I figured it would be an ample opportunity to practice sound.

Quote: Original post by paulecoyote
Audacity has excellent built in noise reduction stuff... / ...It is also legitmately free.

no ... / ... yes.

I would say, research the guns you are trying to incorporate, then look into websites devoted to classic guns. Some may include recordings of that gun firing. If the sounds are of sufficient quality, that should give you source material to practice the next challenge: editing and mastering them to fit your needs and blend together as sound effects.