Possibly the timing chain? My friends timing chain tensioner siezed up and the chain was literally eating through the guides.
Heres a clip of his..
http://media.putfile.com/2000-GT-engine-noise-48-second-mark
It doesn't sound like your buddies, and i recently replaced the timing chain as well, so i know its not that. Someone also mentioned maybe a sparl plug can be foul or injectors might be dirty.
I am gonna try the other suggestons put on here, and see if its an idler pulley.
