I had a new starter motor fitted, after the new one was put on?

I had a new starter motor fitted, after the new one was put on. Every time i turned the key it made a horrible noise then started. the car ran for4days. Then wouldnt start, it just made the same horrible noise when you turned the key but wouldnt engage and start.Thought the new starter motor must have been faulty the shop replaced it(when we took it out the bit that sticks out had broken off.)we're having the same prob again with the horrible noise then it starts after fitting another starter it will proberly mess this other starter motor up as well what could be the problem.Never had this prob before the starter had to be replaced, with the noise.( the man said when he took the starter out he left the dowl in its original place)The car is a renault laguna p reg 1996, 1800, Could anyone help out there please and tell me what is wrong, or whats happenning, why would the starter motor piece off, why would it make this noise before starting?