I bought a Nissan Altima 2015 and its been 18 months since I am using it and have around 17000 miles on my car. Recently I started experiencing engine sound louder than expected when accelerated to 40 mph. Rpm rises upto 3-4000 mph and drastically drops to 1500mph when accelerated at 20mph to 40mph. Is there an issue with Nissan Altima or how do I address this?