isuzu

89 isuzu trooper auto locking hubs. When driven the first time everyday the hubs make a terrible grinding noise in one or both sides. I have replaced the auto locking mechanisms with used ones from the junk yard (seemed to be in good cndtn.) That worked for a while but now its back. About the first 1/2 mile driven daily we have to stop and reverse about 20 feet several times to get the grinding noise to stop. After that they are fine all day and never mess up. This is strange- any input?