A: Sound may blocked by dirt in the inner filter. Try remove the earmuff and take out the filter. You should be able to hear clear sound without the filter. Clean and dry the filter with cotton bud and put it back.
A: 1) Make sure that volume is turned up on your phone after you’ve connected via BT.
2) In the Bluetooth settings on you phone, for each connected device, go into the settings for each Bluetooth device (i.e. click on the gear icon) and make sure that “Media audio” is turned “on”.
A: Issue may caused by the AUX port trigger on the Headphone unit that disabled part of the bluetooth functions. Try insert the AUX connector to AUX port on the Headphone unit few times to disable the trigger.