Here is a link to a test project that exhibits the same behavior. It plays a 'tick' sound once a second for fifteen seconds. The tick sounds get louder during this period. Each fifteen seconds it simultaneously plays a 'beep' sound. The tick sounds the go back to their original volume before, once again, increasing in volume. https://www.icloud.com/iclouddrive/09aUqD5LQctaBKSEO7qvjzCwQ#SoundTest