I encountered an interesting phenomena during the DICTA 2003 conference recently in the Macquarie Uni.
We connected the headphone port from a laptop to a power mixer. Suddenly, a huge buzzing sound came out of the speakers. Everybody was stunned. One of the research scientist from the CMIS disconnected the laptop from its power adaptor. Then, the buzzing sound disappeared. When he connected the power adaptor back, the buzz re-appeared. That was the interesting phenomena.
We tried to put the power adaptor away from the power mixer but the problem persisted. In the end, we let the laptop running on battery.
So, any suggestion of how the buzz was produced and how to eliminate it while still using the laptop power adaptor?