When I am cruising in 5th gear on the hwy at about 2500 RPM I get this vibration under my seat and a sound that I really cant describe in words but I will give it a shot. The noise sounds like VVVVRRRUUUMMMM and then a pause and then vvvvrrruuummm again and a pause and it just keeps doing that until I slow down. I have a world class T5 , aluminum drive shaft and a 4.11 gear 28 spline axle. I know the syncro is about history in 2nd gear and my input shaft bearing is about history but I dont think that is what is causing all the noise in 5th gear at 2500 RPM and higher. Can someone please help me out hear?