Thanks for the computer setup.
Out of interest do you know what the other computer in the conference was using? Squeaking could be related to feedback or echo that is being "looped" through the external speakers and webcam microphone.

It may be worthwhile checking that each computer has the "Voice Enhancements" ticked - these can be accessed by clicking "Audio Settings" at the bottom of the conference.
http://www.nefsis.com/manual/cc-audio-settings.html

Also, checking the exact version of drivers (or checking for any updates) might help - as Logitech have recently released a new version (v2 - Build 13) of their software:
http://www.logitech.com/en-us/435/6333?section=downloads&bit=&osid=13

Otherwise, feel free to contact us (or post back) and we'll be happy to help as best we can.