If it only makes noise when you start it, and the clutch seems to be working fine...then it would have to be the starter is not aligned correctly, or the teeth on it are damaged. Take the starter out of the bell housing, and give the teeth a good inspection. If all looks OK, them it may have been in a bit crooked. Try and line it up so the teeth appear to meet at the right place with the fly wheel teeth. It may have moved after the first start if it wasn't torqued correctly or has stripped threads.
Good Luck!