about 70mph my 04 f350 dually makes a vibrating hum... not sure where its coming from... driveshaft? i do have a 2" lift block on the back, it wouldnt be the carrier bearing with such a small block, would it? carrier bearings usually only vibrate on hard exceleration from my experience... any suggestions? it could even be from under the hood not sure... it is at exactly 70mph... 68mph it doesnt do it....