I have a 1991 Toyota Camry DX and about a month ago, I noticed that every once in a while when I try and start the car, there was a "whining" noise from the engine compartment and wouldn't start. I had to turn the key sometimes several times before it started. I was told there was a bad spot in the starter. So I replaced the starter and everything was fine for maybe a week...now it's making the same noise again. And it's becoming more frequent as time goes on. What's causing this?