Having had a good read of many posts with regard the Harmon Kardon Subwoofer and the buzzing sound, I thought it was time to tackle mine and eliminate the buzz. I expected to rip out the two subwoofer speakers and dump them for new ones....no no no. One article I read stated that the trumpet that is fitted to the speakers often falls out of it's housing and causes the buzzing sound. Sure enough, on closer inspection, mine was not seated in it's housing at all, just sitting loose. Put it back in properly and I noticed the buzzing was gone, replaced the speaker cover mesh over the subwoofer enclosure and a buzzing came back! Arrrgggg, yep, two causes of the buzzing in my car, 1 the trumpet was loose (tested on and loose) made a buzzing sound from the air pressure making the trumpet vibrate in the housing and 2, the mesh speaker cover is plastic on plastic when fitted in it's spot. Silicon between the plastic cover and the housing and I have a buzz free subwoofer. Hope this is useful to those wanting a possible way of eliminating the buzz for no dollars!