Sounds like your drive belt needs replacing. The old cassette car players were prone to this problem, especially in very warm or very cold climes. An aging main drive belt will slip and the direction sensor will be tricked into it's "end of tape---switch directions" mode. No easy in-dash repair, sorry. Player will have to be removed and disassembled to reach the belt. A good tech will also check the other drive belts, drive wheels and clutches while he's in there.