DIAGNOSIS The monitor has 2W x 2 speakers. They are for basic system sounds only. They lack bass and volume.
FIX Do not use them for media. Get external speakers or headphones. To disable them, press the menu button. Go to System > Audio > Volume. Set it to 0. Or, in your OS sound settings, select a different output device.
IF THAT DIDN'T WORK If sound is crackling, check your audio cable. The monitor gets audio via the HDMI or DisplayPort cable from your source. Ensure that cable is firmly connected at both ends.
HEADS UP You cannot adjust treble/bass on the monitor. The audio quality is a hardware limitation of the small drivers. Use externals.