vibration / hum/ grind from rear end

[poolguy435]

Over the summer my expy has started to make this noise. It only occurs around and over 60 mph. More so around 75-80. I noticed the pinion seal has been leaking but i'm not sure how long. It is definatly coming from the rear of the truck not the front. I can feel the grind in in the peddal when you level it off. Any ideas or suggestions? This is my daily driver and it does go on 700 mile trips to Maine at least once a month. Thanks Nigel

 

[bcburlette]

Did you ever find out what caused this? mine just started doing it.