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Intermittent Grinding Noise in 4WD Highlander - dealer no help

My wife’s Toyota Highlander has full-time 4WD. A few weeks ago she began complaining about a noise. She said it happened every once in a while when she accelerated from a stop, or after coasting in traffic, she then applied the gas.



When she took it to the dealer, they couldn’t replicate the noise during a test drive, and sent her on her way. The noise persisted in happening.



Then she had me drive the car on a weekend shopping trip. Sure enough … eventually there was a high pitched metallic grinding sound, like gears grinding, when I touched the gas, and a slight pause before the car moved, or picked up speed. It sounded like it was coming from under the middle of the car.



Back to the dealer. This time they heard the noise on the test drive. Then, they checked the brakes! Then they did a “zero point calibration” on the ECM … . No noise on the test drive, thank you, goodbye.



Well, needless to say, the noise is there again! My wife also now feels a slight pulling to the side when the sound happens. This is getting worse. I suspect there might be something wrong in the unit that keeps all four wheels in synch with each other. ( whatever that’s called ) Whether it’s entirely mechanical, or computer controlled, somethings not engaging properly.



Any suggestions on how to handle this will be very much appreciated. There is an independent shop down the street that does decent work. What should we ask them to check that the dealer might have missed?



What’s the risk of totally screwing up the drive-train if this isn’t resolved soon? We want to take a Spring Break, but are reluctant to leave town with the car in mechanical limbo.