It is important to ensure that the volume of your aux playback device is not set too high. If the incoming signal is too loud, this will overload the aux input of your Alesis drum module, resulting in distorted sound.
Keep the volume of your playback device at around 70-80% to retain the clarity of your backing track's audio and avoid overloading the drum module's aux input.
If you are using a smartphone, please use the volume controls which are directly on the phone itself.
Once you have correctly set the volume of the playback device, you can freely adjust the output volume of the module to a level that is comfortable for you.