VW Jetts 2000 GLS VR6 Noise Problem

Hello, I bought a used VW Jetta 2000 VR6 Yesterday from a dealer (not VW). Though I have heard a slight noise (so't of bearing screeching) I took the dealers word to be usual for a car with 140000 miles on it. But after driving it for about 300 miles the noise has become really loud & audible from outside without the hood open. I am wondering if this is something serious. Check Engine Light also turned on now and wouldn't go off. Is it something to do with timing chain or bearings for one of the belt pulleys gone bad? I can return the car immediately if this is something major. I would appreciate if someone can let me know.
Thanks.