My car just started making a very weird whining sound, like an ambulance or fire truck sirens. My service engine soon light is on, for a P0420 code, so I don't know if that left untreated could have caused my engine to make weird sounds? Or maybe I just need to replace my serpentine belt.

 

It could be the belt, but it could also be the alternator bearing or the a/c bearing or the belt tensioning pulley bearing.

 

I really hope that it is something simple like one of those things. I had another guy tell me today that it could be a rod bearing. But I think the car would be driving a little bit rough, or really rough if I spun a rod bearing.

 

Problem solved, it was the alternator pulley and bearing, its fixed now, thank you Dennismik for your suggestions.

 

Spoke too soon, the bearings in the alternator are smoked, the pulley is completely fine, looks like I'm gonna have to spend a lot more then I originally expected.