It does it in beat with the bass. At first I thought it was picking up vibration but no, the noise seems to come from inside. Also I hear it only when the volume is like 75%. So there's a lot of music sound and though it's audible only when I put my ears near the pod probably it's not just some soft 'tsk tsk' sound considering the rest of the noise... But if I go 2 feet away it's not audible because it gets muffled by the music. The more bass there is, the more it happens, in beat. Is something going to go wrong?