Check that all components are plugged in and turned on.
Check all interconnecting cables.
Check that the subwoofer is connected to the sub out (or other appropriate output) on the receiver/processor/amplifier.
Check that subwoofer output is enabled in the receiver/processor's setup menu.
Make sure the sub's level control is not turned down.
If the problem persists, contact your dealer.
Muddy Bass
Check placement. Try moving the subwoofer closer to the front and side walls.
Check the type of feet that are being used. If available, try installing the ETC spikes.
Decrease the volume level.
Check your processor setup.
If the problem persists, contact your dealer.
Hums or Unusual Sounds
Turn the subwoofer off, unplug all signal inputs, turn the subwoofer back on and turn up the level. If the problem disappears, the hum is originating elsewhere in your system.
Connect the sub to the same AC circuit as the receiver/processor.
If operating in wireless mode, move the sub away from microwave ovens and/or any devices that use wireless technology.