How To Minimize Background Noise During a WebEx Meeting:

When participating in a WebEx audio conference, avoid background noise whenever possible.

Turn On Mute

It is a good practice in general to mute yourself when you are not speaking (just remember to un-mute yourself if you do need to speak).

Avoid Activities that Can Be Picked Up by the Microphone

Avoid typing, sorting papers, eating, or performing other actions that can be picked up by your computer or phone microphone.  Some of these activities can generate significant noise.
Note:

• If you are using your laptop and its built-in microphone to join the audio conference, typing will be readily picked up your microphone and heard by all participants. 
• If you need to perform an activity likely to generate noise that will be heard in the audio conference, be sure to mute yourself in the audio conference. 

Use headphones, headset, or handset

If you are joining the audio conference using your computer (VoIP) and are using the built-in microphone and speakers of your computer, this can create a feedback loop which can overwhelm the built in echo cancellation and cause a loud echo or other feedback effects.  Using headphones or a computer headset instead of speakers is the easiest way to prevent feedback loops. Similarly, if you are using a speaker phone, depending on the quality of echo cancellation built into your speaker phone, it may create echo or feedback loops. Using a handset or headset is the simplest way to avoid the possibility this problem will occur.

Check firewalls, proxy servers, and other network or hardware restrictions

If you have network or hardware restrictions in place on your computer or a local network, such as firewall software, proxy servers, or router traffic restrictions, these may interfere with WebEx's ability to send and receive audio (as well as other functions).  If you have such restrictions in place and encounter audio issues, consider disabling them temporarily to see if it improves performance. 

Switch off your cell phone

Consider turning off your cell phone for the meeting.  Some cell phones may create interference with your speakers or microphone.  If you prefer to switch off the ringer on your cell phone, be aware that vibration from a cell phone can still be very loud if you are using your computer's built-in microphone for audio and your cell phone is sitting on the same desk as your computer.

Locate the microphone properly

Try to keep a constant distance between your microphone and mouth to provide consistent audio for listeners. If using a headset, place the microphone in front of your chin, not in front of your mouth, to avoid heavy breathing sounds.