In 4th and 5th Gear around 2,000rpm i can hear a slight humming noise and can feel the vibrations slightly through the drivers side floor and pedals. As i speed up the sound gets louder and then goes away. First and second are silent and third is quieter but still noticeable. I have recently changed driveshaft however the noise was apparent before. There is fresh oil in the gearbox, 75w 90