What is background noise?
When recording a person speaking, your aim is likely to capture the speaker's voice and nothing else. Anything else captured in the recording (a door slamming, a fan running, someone else talking in the background) likely constitutes unwanted background noise. Unless it's been purposefully included, it will likely prove distracting to your listeners. Podcasts with unwanted background noise often sound less professional.
What can I do about it?
You'll first want to take a look at your recording environment – make sure you're recording somewhere quiet where you are unlikely to be disturbed. Eliminate sources of noise, such as fans and ringing phones. Make sure you don't hear any hum or buzz from your microphones, or the microphones of your guests – you can do this by making a quick test recording (alone, or with guests) and listening back in Cast's Editor.
If you find that you've made a recording that does have background noise, Cast's Editor and noise reduction features may be able to help salvage some of these recordings.
If your background noise is of a periodic nature (a phone ringing, a door slamming), your best bet may be to use Cast's Editor to cut out the offending section.
If the noise is a buzz, hum, or hiss that continues throughout the entire recording, read more about Cast's noise reduction feature to see if it might be able to help.