On my 2004 2500 4X4 CD, the front diff has been making some high pitch noise like a bearing going and it only happens at 65 mph, any lower the noise stops, but then speed up to that speed and the noise comes back. Speed up to 80 and the noise increases slightly. One person I know said it sounds like the fuel pump could be cavitating, but shifted truck into neutral at 70 and noise stayed the same, and the rpm came down below 1000, so would that eliminate the pump. Noise is annoying and I can't pinpoint what it could be. Any thoughts out there, or similar problems had by anyone. Any info much appreciated. Thanks
Troy

 

Could it possibly be the front driveshaft? That's a common problem at around 65 - 70 mph. Try pulling it out and see if the noise goes away.

--Eric

 

I too would assume driveshaft before gears