I just bought the ProMedia 2.1 from Costco too and I'm having the same humming issue. I'm getting a fairly noticeable humming sound from the subwoofer. I have an older ProMedia ( 6+ years old) I am trying to replace because the right speaker is starting to have some rattle/cracking. The older unit has no humming from the subwoofer board on the back ( I also noticed the newer version of the ProMedia subwoofer is way heavier, so I'm assuming they changed the woofer design). Just curious "The Inspector," how does the ProMedia sound compared to the Logitech THX Z623? Is the Humming noise normal? I don't think it is... Can anyone at Klipsch confirm this is normal behavior?