1997 Volvo 850 "pic shaking back forth" Questions

...shaking back and forth which appear to be making this sound. Also the A/C is not working all the time which also kinda directs me to this same area. A guy at work mentioned a tension adjustment or ...

...shaking are caused by this. If you live in the cold weather, winter does a number on your car along with potholes and bumps that you drive over.a good habit, get your tires rotated every time you get ...