car vibration between 40-45 mph.

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I have a 2006 Suzuki aerio sx awd. The car has 39,000 miles on it and a vibration between 40-45 until you switch it into overdrive. i have taken the car to the dealership multiple times. after they replaced all 4 car mounts nothing changed. they finally sent someone down to take a look at it and he said its normal, and that its a manufacture problem, and theres nothing they can do. however, i ended up taking it to a transmission place. turns out the transmission was breaking. They checked the oil in transmission and the metal got mixed in and my car would not move in any gear. suzuki then replaced transmission and the vibration is still there. I'm not sure what caused the transmission to brake, and worried its the vibration that caused the damage.