Loud vibration noise in reverse (2007 Corolla!)

Joined: Nov 02, 2007 Posts: 2

I have a new 2007 Toyota Corolla. I bought it in Feb. and it now has 9500 miles on it.
Earlier this week I came out from work and when I put it in reverse to back out of a parallel spot, it made this really loud noise that sounds almost like it is inside the car towards the back seat. It seems a little worse in reverse with my foot on the brake (than when I am actually moving in reverse). It sounds like a loud vibration and it localizes just under the floor mat in the back seat slightly to the passenger side of the hump that splits the feet area.
It persisted at the first stoplight when I put it in reverse to test to see if it was still there, then it was gone for the remainder of the day.
I called the dealer and talked to a service technician who said it didn't sound like anything obvious /that is common and that unless it persisted every time I put it in reverse, they would have trouble figuring out what it would be.
Then yesterday after the car was parked in a ramp all day it did it again. Then again tonight after the same circumstance. I live in MN and it is cooler now... it has been in the upper 40's all three times that it happened. It is not doing it in the morning when I back out of the garage, only after it has been sitting outdoors, so I think temperature is a factor. After I drive a few miles, I can't reproduce it. During the first few minutes after it happens though, I can hear a rattling when I go over bumps that sounds and localizes very similarly, but this also seems to then disappear when the car warms up after driving a short distance.
It is a very loud sound and I can feel some vibration through the carpet on the floor on the passenger back seat when it is happening. If it was just something loose that is vibrating, why would it go away? why would it only be in reverse? (and/or possibly triggered by road bumps?)
Any idea what is going on?
I am going to call the dealer again on Monday and get an appointment for them to have the car for a day where it sits outside and they start it up, so that they can reproduce it.
This is extremely irritating for a car that isn't even a year old, especially a 'reliable' Toyota which is why I went with this maker!!
Any insights/help is greatly appreciated.

Joined: Feb 13, 2008 Posts: 1

My wife just bought the same model car and guess what?! It has the exact same problem and I figured it out.

There is a flimsy looking cross brace under the exhaust pipe approx under the middle of the back seat. The pipe goes over this brace then immediately curves down then back toward the rear of the car. When the temp is low, the exhaust pipe contracts and pulls its self into this brace. When you put the car in reverse the engine rotates and pulls the exhaust pipe even further and then starts vibrating against it. When you put the car in forward the engine rotates slightly in the opposite direction stopping the noise. After warming up the pipe expands and the noise goes away. It does not appear to be anything to worry about in the short term but it should be taken in to the dealer. I doubt it would wear a hole in the pipe since it only happens when it's cold and opnly while in reverse, but it could drive one crazy from the noise. Smile

Hope that helped