Q: Squealing in 1992 Cadillac DeVille with engine off

Hi. I have a 1992 Cadillac DeVille with a new engine, the rest of the car is pretty done for. I live in New England and there is a lot of rust. The gas tank was leaking but we managed to patch it. There is an oil leak and a coolant leak as well. I took it for an oil change and asked them to drive it and diagnose the squealing. They said although the brakes were good the calipers were bad and thus squealing on and off. Recently I noticed a different squealing/alarm sound coming from inside the car. It is continuous and continues even when the car is not running. It does not drain the battery, though, there is a problem with the battery draining. The alarm sound is almost unbearable and if I could find a way to turn it off. I plan on selling the car soon and upgrading so I only need to get by with it for a short while longer. Thank you

My car has 94000 miles.
My car has an automatic transmission.