How to get rid of vibration under drivers seat and steering wheel?

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I have purchase a 2014 Kia Optima. I have taken my car in for an oil change at the same dealership I have purchase the vehicle. When I received my car back there was a constant vibration under the driver seat and steering wheel. The dealership does not want to change my vehicle stating this is normal but this vibration was not there until I took my vehicle for an oil change. Please Help