Lanos Motor knock

My girlfriend has a 2000 Lanos. It has just started knocking pretty loud when at higher RPMs. Anyone have any advice on where to start. I think the car has about 50,000 miles on it. Any help would be appreciated. It is the 1.6 DOHC sport version.

edit"
Changed the oil in the car this afternoon and took it for a test drive. The sound is more of a tapping sound. It sounds like a woodpecker on an aluminum can. I am lost and have no idea. Any Help??