BACKSEAT VIBRATION DRIVING OWNER BATTY

Dear Car Talk:

I get a vibration noise behind the back seat area when the car is in drive, the lights are on and I stop at a light. If I turn off the lights and put the car in park, the vibration and sound both go away. I am living and working in Japan, and my car is a 2010 Toyota Paseo. I’ve had it only two months. I removed items from the trunk to see if that is the problem, but I still get the vibration. Please give me some solutions. It’s driving me nuts. If I can’t get rid of the noise, I will have to get rid of the car! -- Mike

Well, now you know why the last guy sold it, Mike. You also know where to find him. So you can go visit him in the psych ward, and ask him what solutions he already tried.

Since it’s coming from the back seat area (the car’s, I assume, not yours), it’s most likely to be something fairly benign, like the exhaust pipe vibrating against the underside of the car.

When you’re stopped at a light in drive and your headlights are on, the engine speed is dragged down. It could be that when the engine is turning slowly and the geometry of the exhaust system is just so, the pipe between the catalytic converter and the muffler moves up just enough to touch the bottom of the car.

When you put the car into park and remove the power drain of the headlights, that results in an increase in idle speed and a slight change in the angle of the engine vis-a-vis the exhaust system. That could be enough to make the vibration go away. As an experiment, you might even be able to make the noise go away temporarily by holding your left foot on the brake and touching the gas pedal lightly.

But since the problem is pretty easy to reproduce, it should be a piece of cake to solve. Just take it to a mechanic, put your foot on the brake, put the car in drive, turn on the headlights and get the vibration going. Then the mechanic can grab the tailpipe, using a cloth or a pair of gloves, and see if he can stop or even just change the vibration.

If he can -- and I suspect he will be able to -- then it could be something simple, like an exhaust hanger that broke off. Or maybe you bent a section of the exhaust pipe when you drove over those sake barrels.

If he can’t find anything wrong with the tailpipe itself, then you could have one or more worn-out or broken motor mounts. A broken motor mount also can cause the exhaust pipe to shift, because it allows the engine to move too much. He can test that, too, while you’re in gear, by using a big pry bar against the engine and seeing if the engine moves more than it should or if shifting the engine changes the noise.

But go get it taken care of soon, Mike. We don’t want to read that you went Japan Post-al on us.

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