The ‘input volume’ to the transmitter base unit is set too low. This must be set at a proper fixed level.
Explanation: there are two volume settings; the (main) volume control on your music source and the volume control on the Headphone unit.
The Volume control on your music source controls the input volume to your wireless headphone base/transmitter unit.
The volume control on your headphone controls the actual listening volume.
Solution:turn up the volume of your music source to the highest acceptable undistorted level. If possible, always connect your wireless headphone base/transmitter unit to an adjustable audio output (usually any headphone output jack).
In case of a HiFi stereo, set the main volume knob at a fixed position.
In case of certain TV’s, the headphone jack output level can only be adjusted after accessing the TV on-screen menu.
Note: adjusting the listening level should be done at the headphone itself only! Do not adjust the listening level using the main volume knob on your music source, as this will compromise the signal to noise ratio and might introduce unwanted background noise.