External HDD Causing WiiMote Interference, What!?!

[scummos]

"Interference" is unlikely, the wavelengths aren't similar in any way. There could another kind of correlation, tough: HDDs need very much power, and USB often struggles with that. So in case your HDD has no external power source but gets its power through USB, maybe the voltage drops a bit when it's on, and the bluetooth dongle has less power available for sending.
Just a wild, guess, tough.