I hear what I refer to as a metal-tap sound in audio dialog. Meaning when there is loud speaking in the center channel. I had thought this was to do with a center channel acoustically hitting the glass behind it. However, I was at a hotel room, with a completely different configuration, and playing a completely different dialog-audio, and experienced the same 'metal-tap' sound. Is it possible that this is a fault of lower quality MP3 and dialog.. or lower quality Video and Dialog? That a metal-tap sound will emerge. My ears are very sensitive to higher pitches, and will pick up ambient noises.