What could be causing the noise in my engine when driving from an incline to a flat surface?

Dear Car Talk

Dear Car Talk | Nov 01, 2000

Dear Tom and Ray:

We have a '95 Toyota Corolla DX with 77,000 miles on it. After driving slowly up an incline and then going onto flat ground, the engine noise changes. The noise sounds like pebbles or sand particles floating at the bottom of a vessel. This happens, for example, when I go up my driveway and then into the flat garage. I only hear this noise when the car is moving slowly. When cruising, the engine purrs smoothly. Any ideas? -- Prasad

RAY: I would guess it's an exhaust system noise, Prasad. When you drive up a hill, you shift the geometry of the car's suspension.

TOM: And then when you reach flat ground, you shift it back again. My guess is that during this transition, some part of the exhaust system touches the underside of the car and vibrates a little bit.

RAY: It might be happening at higher speeds, too. But at higher speeds, all the car's other creaks and groans, plus the wind and tire noise, drown out the exhaust noise, and you don't hear it.

TOM: My guess is it's benign, Prasad. But if you want to put your mind at ease, try to duplicate the noise for your mechanic. The only hard part will be finding a mechanic whose garage is up a hill from his driveway. Good luck, Prasad.

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