My iMac just made a pop-crackling sound, and all the sound died! It was during a video chat. No sound effects, music, or anything would play! After I closed the video chat, I heard another "pop" and the sound returned! Should I be worried? Also, I have intermittently heard crackles (probably once a week or so) from the computer, not affecting the sound. Cause for concern? It's about a year old.