This is caused by the volume synchronizaton system in the iPad. When you switch off the iPad with click sounds activated, it sends the click sound to the Go+Play, also ordering the Go+Play to increase volume to maximum. The hiss is a result of the Go+Play Wireless being at full volume. As soon as you re-start your music playing from the iPad, volume is back to normal music use. If you do not switch the iPad on again, the Go+Play goes into standby after a few minutes, and the hiss disappears. You can prevent this problem by de-activating the click/alarm sounds on the iPad.