It turns out, after much trialing and errors, that the buzzing my interlocutors can hear whilst I’m iChatting with them from my G3 iBook is caused by the Airport card in my G3 iBook interfering with the microphone in my G3 iBook (goddam G3 iBook!). So this also affects Skype, X-Lite or anything that uses microphone and the network at the same time (unless I use the ethernet to connect).
The solution seemed to be to get a bluetooth headset. But the OS X bluetooth stack turns out only to support headsets if you get the D-link DBT-120 (not the DBT-122 as I found to my cost).
When I finally got a DBT-120 I dutifully tried to update the firmware using Apple’s Firmware Updater which kind of appeared to be doing something for a bit and then said idle. And when I tried to quit it said “firmware not updated”.
Well, it seems the trick is to zap the PRAM, folks. Then the firmware update will work and you can happily iChat away secure in the knowledge you’re not inflicting buzz on your buddies.
So I’m happy wandering round like a nerd with a dongle-thing (HBH-600) in my ear (the range is abysmal though, so I don’t wander far), but what a lot of hurdles I had to jump through!