To get the best sound quality out of your iShower2, you should always set your phone or mobile device volume as high as possible once it is connected.
If you are hearing audio distortion, the EQ settings on your phone or mobile device’s music player may be too high. For example, if you are playing music from your iPhone and you would like to reduce any full volume sound distortion, go into Settings > Music > EQ and select "Bass Reducer." There are many other settings under EQ that can be adjusted to modify the sound that is transmitted to your iShower, so try out the different presets and see which one sounds best for you.