Starter problem

I friend has a 70 Duster that he has owned since new. It needed a new starter so he bought one and I put it on. The old starter made a noise just as the engine started and the key was returned to the run position. Thought it was part of the problem. The new starter does the same thing....it is a 225 slant six. And yes I did put the sheet metal spacer back in....Anyone else had this problem in the past? Thanks in advance.