Use a high-quality 3.5mm auxiliary cable. Frayed or cheap cables can create static, which translates into uncomfortable electrical interference.
If you want absolute control over your sessions, you can easily create custom audio files using free digital audio workstations (DAWs) like . Step-by-Step Custom Creation in Audacity: e-stim 2b audio files
E-stim is safe when rules are followed, but improper use of audio files can cause injury. Use a high-quality 3
Check that your 3.5mm audio cable is fully pushed into both the player and the 2B box. A partial connection usually drops one of the stereo channels. Alternatively, check if the audio file itself is balanced to only play on one side. e-stim 2b audio files