Cat 257b problems, tracks squeal and lock up

I have a Cat 257b skid steer with tracks. Sometimes when moving the tracks start to squeal and lock up like a brake is being applied. Not sure if it's the left, right, or both tracks locking up. The parking brake light does not come on and the hydros still work the bucket, (elimnating the lap bar or seat switch in my opinion). It will not move in forward or reverse until I lift the lap bar and then turn off the parking brake. Then it will move again sometimes and other times it takes several attempts, or I just have to turn it off and let it cool down. Usually after cooling down it will work until it heats back up then it does the same thing. Some days it happens a lot, other days it does it some, and some days not at all. Seems to be getting worse latley. Any ideas would be greatly appreciated.