Looped sound Hiccups

I have a sound file I wish to loop like the engine of a vehicle. The sound I have is 1 second long and it is a .wav file. I'm quite certain the file is cut to be seamless, it loops perfectly in Audacity.

I'm calling the sound with this code:

let playEngineSound = SKAction.playSoundFileNamed("engine.wav", waitForCompletion: true)
let engineSoundLoop = SKAction.repeatActionForever(playEngineSound)
self.runAction(EngineSoundLoop, withKey: "engine sound")

I use "withKey" to be able to cancel it later. The Sound comes out fine but there is a small but distinctive hiccup where the sound seems to be reloading or waiting for the other to stop completely before starting the new loop.

Any help would be much appreciated!