2001 Mitsubishi Eclipse GT Spyder 5-Speed Manual suddering at high rpms?

I just test drove the car stated above. As with all test drives, I put the car through it's paces. I found that at about 4500-5000 rpms the car made a shuddering noise coming from somewhere in the engine compartment. The owner (knowing very little about cars) claimed that someone had told him that it was a feature Mitsubishi included in their cars to stop from over-reving the car. However, the car doesn't redline until 6000, making me skeptical. Anyone else have this problem or know what it is?