About a week ago, I heard this scraping noise and thought I was dragging a branch or something. It happened a few times, then stopped. I checked and saw no branch or anything hanging under the car, so I took it to my mechanic. He put it on the lift and couldn't find anything obviously wrong. He wanted to replace the bushings (?) on the rear wheels for around $300 but I said to hold off as the noise had stopped. I haven't heard the noise since. Any ideas? Has this happened to anyone else? I have a 2006 Mazda3s sedan. Thanks!