Game skips frames when a sound is played on iOS

Hello.

I'm working on my next iOS game. When we added sounds to ball movements, the game skips few frames.

The code I use for playing an audio is:

 AudioSource.PlayClipAtPoint(marbleMoveAloneSounds[Random.Range(0,2)], Camera.main.transform.position);

The random is to have different sound each time I move a ball. The problem seems to be very negligible when I play the sound one (when I move one ball at once) but it becomes very clear when I Play 3~4 sounds (with the same line code above) as I move 3~4 balls together.

The game contains other sounds, but none have this problem showing.

Note that the problem doesn't exist on my Galaxy Nexus but it shows on iPod4 and iPhone4

Please help.