Amanda, any time you have intermittent problems with your vehicle, this is a sure sign of a potential PROBLEM OK? now when these things happen, obviously something is WRONG. so it is best to get to a repair shop, while the car is still functional, and especially when it is running badly this is the time to go to a shop and get a repair estimate. problems generally do not go away,, and always get worse, for future reference, by getting the vehicle to a shop before it breaks down, you can often minimize the down time, and the potential of more damage, by being proactive and getting another opinion besides your own.a bad screech sound is bad, not good, I am hoping you have a bad alternator bearing or something simple, But at this point you need a mechanic, lets hope ignoring the warning signs for the last few months turn out to be a bad part due to old age. best of luck, good luck