I need help with removing the faint knocking sound in the background of the sound recording. I’ve tried cutting out parts of the audio but it ends up being way too short (0.3 seconds) and the looping of the sound is very noticeable. Is there a way to do this without reducing the length of the sound file? I only want to keep the ‘buzzsaw/roar’ sound. If anyone can edit it for me I would greatly appreciate it. Thanks for your time. 
Open the file with audacity to hear it properly.
Instead of cutting it out, you can silence it. Drag-select the offending sound and Control-L. You can also paste good sound over it. That’s probably your best bet.
With that kind of effect, I bet nobody notices. You’d never be able to do that with an opera, for example, but jet noise is probably do-able.
Do you know what happened? Why did the recording become damaged? Or the performance really sounds like that and you didn’t like the capture?
Koz
I was going to suggest Noise Reduction, but you don’t have the offending sound there by itself, so that wouldn’t work.
Koz
There is free audio processing software called SPEAR which can do this job …
The buzz-saw noise you say you want is constant throughout, whereas the other sounds are not.
That difference can be used to discriminate wanted-signal from unwanted-noise in SPEAR.
Do you have a neat, orderly list of all these add-on programs?
Koz
SPEAR is a stand-alone audio-editing program , not a add-on for Audacity , [ it’s available for PC & Mac ]
SPEAR is suited to the brief here : extracting a constant-tone from noise,
but for tasks involving speech the results from SPEAR sound very computery , (unusable IMO).
That method works quite well. I have no idea what happened to it as I didn’t create it. The original file was a lot worse (before I edited it).
Most such add-ons are VST plugins, so in principle yes: http://wiki.audacityteam.org/wiki/VST_Plug-ins.
Gale