Blabbermouth has an extensive report on the issue, here are some highlights: Norwegian music industry magazine Faro Journalen downloaded one of the versions Universal Music released to the press via its digital promotional database. The magazine then sent the file to Lasse Svendsen, editor of Norway's hi-fi magazine Lyd & Bilde (Sound & Vision). Svendsen was shocked by what he heard.
"Oh my God, this is unfortunately a classic example of how bad things get when studio technicians and musicians gets to play with expensive compressors and limiters," he said. "The file is a 313 kbps AAC sound file, which isn't necessarily that bad, but someone has chosen to maximize the volume with a compressor, so much so that the whole sound file just sounds like mud. The cymbals sound like broken glass, the drums like trees cracking, and the guitars � which are mixed equally loudly � sound like someone shoved a screwdriver into my ears."
Ouch! read more and some Metallica fans reaction (including one fan banned from Metallica's message board over posts about this controversy) at - Blabbermouth