My 2010 mustang 4.6 has a vibration if I get up to 75 mph and let off gas. As it slows to 70mph and 2200rpm I get this drone vibration through that range coming from front of car. If I give gas it clears up but if I push clutch in it also goes away. Dealership said normal but I don't think so. Any help would be much appreciated. All stock car only has 2800 miles. I'm wondering if it's pinion angle or harmonic balancer.