[LAD] Looking for the cause of pulsating noises

Hello, I have developed an audio recording application for Android, and a user is reporting a weird noise issue. There are near-zero chances that this comes from my code, and I'm looking for the possible cause of these noises. Here is the sample, it's a musical flute and violin recording: http://sound.samalyse.org/tapemachine/pulsations.wav Listen carefully and you will here small pulsations. I've also asked him to record a 440Hz sine. This one isn't distorted: http://sound.samalyse.org/tapemachine/record440hz.wav I suspect that this is a hardware issue, but I'm no expert so I can't really tell. The phone is an HTC Incredible, which unless I'm wrong, means that the sound components are embedded into a Qualcomm Snapdragon QSD8650 chip. One other is that, although Android is a linux-based system, and use alsa underneath, there's a terrible high-level Java API, which is full of various problems which I have worked around to obtain that kind of quality. Thus, I can't really tell what happens in there. Have you already heard such things, and know what the cause, whether hardware or software, is likely to be? -- Olivier