[quote name='BottomEndian' post='935679' date='Aug 25 2010, 10:00 AM']Usual suspects tend to be mobile phones, fridges or occasionally WiFi networks (especially if there's something transmitting or receiving anywhere near the bass or amp). Sounds like you've eliminated those, though.
Baffled. [/quote]
I do use an Airport Extreme base station for my Wi-Fi, but this is in a different room. I have noticed there are quite a few different networks nearby when I do a search on my mac. Could this be the cause I wonder?