I'm not an expert with cars, so I know my vocabulary is very limited. Basically, my car, an automatic transmission, has been making strange noises and isn't as easy to drive. It might be a coincidence that it started doing this after I got a couple serpentine belts and the O2 sensor changed. Instead of the usual sound when I start driving, there is a more high pitched whine, especially when I'm in reverse. Also, using the gas isn't as smooth as it used to be. Maybe it's an engine thing. I can hear it as the gears are shifting. It's almost like something is straining. I have noticed it doesn't seem to be as loud when the car has warmed up. That's about as specific as I can get. I hope someone can help me figure out if there is anything wrong with my car.