If I plug my 13" mbp to my external speakers via minijack, everything is fine. If I plug it to my tv (Monoprice displayport + USB) -> HDMI adapter and I start playing any sound, a loud buzzing sound comes out of my speakers. if I stop sound playback, the buzzing sound persists for a while, then disappears. If I unplug the displayport and leave only the USB (which is used to power up the monoprice adapter) plugged in to the adapter, the buzzing sound still comes out. if I unplug the USB and leave only the displayport plugged in (the adapter is now OFF), the buzzing sound still comes out. If I plug in headphones instead of external speakers, there is no problem. This problem does not happen when I use my work's Macbook pro 15". It also didn't happen with my personal laptop before the past few days. Why is this happening? My laptop is still under warranty but how do I show the problem at the apple store? Any ideas?