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I have an 04 Sentra 1.8L 5 speed with a suddenly recurring starting issue.  About a month ago when I hit the key I get that lovely "whirring" sound from the starter.  At 60,000 miles I figured the starter was shot, so I replaced it.  Everything was fine for about a week, and then I began having incidents where the starter was still engaging for 2 or 3 seconds after the engire started.  It was like a power surge to the starter.  Now it is doing it again, the starter just whines but does not engage.  I happened to have another used starter in my garage so I swapped it out again and it ran fine for another week or so and then started spinning again.  Are there shims with this starter that I need to put on to make it catch?  Or is there some kind of electrical issue thats frying them?  Thanks everyone!