Okay, I just encountered my first problem with the DM4T --
I've noticed that everytime it makes any sound, it emits a short high-pitched click first. This occurs before all notification sounds (like when I plug in my iPhone, start playing an MP3, or receive an instant message).
I'm definitely not an expert, but I had an HP hdx16 for a while, and it used to make a clicking sound before playing sounds intermittently. I eventually figured out (after a lot of net searching) that there was a power setting that turned the speakers off after a set period of time, so when you played a sound, it would turn them back on with a "pop" or "click" before playing the sound. There should be a power management setting for the sound device or something, I would think. So you might want to try that! Good luck!