I recently noticed a crackling noise inside of my 2011 Macbook Pro - like a rain stick (one of these http://youtu.be/riQNqpwXkvE?t=34s) - whenever I tilted it. The screen cracked years ago but never got worse. I realized once the noise started that the tiny glass bits, had been tightly packed at the crack's epicenter, had fallen out. I hypothesized, and two IT folks confirmed, that these tiny shards had probably fallen inside near the hinge. Clearly several tiny, loose objects scraping around. The repair shop said they would fix the screen and clean out the glass inside. I got it back today and it seemed repaired. Screen looks perfect, and I heard no noise when I tilted it at the store.But now that I'm home and it's turned on, it's doing it again! What on earth could it be? I'm taking it back in tomorrow, but since they got something wrong, I'd love to hear another hypothesis so I could tell them what to look for. It's somewhere beneath the upper keyboard and has spread out a bit since it first happened, though I try not to move it. Aside from the sound, the machine functions normally. What could cause this "loose bits" noise only when it's on?