tgarison,
Change both the fluid and filter every 50,000 miles if the vehicle is mainly driven under one or more of these conditions:
- In heavy city traffic where the outside temperature regularly reaches 90 degrees Fahrenheit or higher.
- In hilly or mountainous terrain.
- When doing frequent trailer towing.
- Uses such as found in taxi, police or delivery service.
If you do not use your vehicle under any of these conditions, change the fluid and filter at 100,000 miles.
I agree with the others, it may be the pulleys. A certified technician will be able to offer a more accurate diagnosis after a physical inspection.
Louis
GM Customer Service
