@gazbadman: This could be related to your current Notification sound, as some come through louder than others. To check, please head to Settings > Sounds and vibration > Notification sound, then adjust the slider at the top of the screen so it plays a sample of the current volume. Is the volume level the same as when a notifications comes through? If so, you may wish to try changing your current default sound, to see if you notice an improvement.
