When going more than 55MPH car (mainly engine compartment) shakes slightly. But if I try to accelerate the car shakes more and more violently the higher the RPM's. Car doesnt shake at all below the speed of 55MPH or when reving engine to redline at any speed below 55MPH. Please assist on what could be the issue. Already have had the tire's balanced and a tie rod replaced and had it aligned.