Annoying hum

[David Brostoff]

Whenever I am on the telephone and touch the case of my Ti 667 II (as 
when I am using the keyboard and my palms are on the palmrests), the 
person I am talking to and I can both hear an annoying hum coming 
through the phone. I have tried a different telephone and get the 
same results. I never had this problem with previous plastic-cased 
PowerBooks (180, 540, 5300, WS II).

The hum goes away if I unplug the phone and just run it on its backup 
battery, but this removes most of the phone's functionality. It also 
goes away if I unplug the PowerBook, but this requires endless 
charging and swapping of batteries while I am working at my desk.

By the way, the phone and PowerBook are plugged into two different 
wall outlets.

Any suggestions?

David Brostoff