When I go a certain speed, 30mph for example, and then lay my foot off the gas pedal, my Maxima decreases its speed. At about 10mph, there is a sound that can be heard and a bump that can be felt. The bump feels like the car is pushing itself forward or perhaps backwards. This may be a transmission problem. Is this something I should be concerned about or is this normal for a Nissan Maxima SE. I only had this car for a week.