Having a strange issue. Im getting a high pitched vibration sound (almost like metal on metal) when on the highway while accelerating. The sound is sort of like the squeal you get when you engage the starter when the engine is already running. Noise is not present at idle or below 60 mph. Only when I am on the throttle above 60 mph does this happen. Confusing to me as I would think it would EITHER be RPM related or Speed related but not both. HAVE to be above 60 mph AND under load. As soon as I release the gas the noise stops regardless of speed.

 

U-joints? check that out.

 

Turned out it was the rear diff. Bad bearing or something is letting the whole differential angle itself upward when torque is applied to the driveshaft. Bad angle is most likely causing the grinding inside. Thanks for the reply.

 

I'm glad you found your problem, let us know how it goes.

 

Ended up ordering a refurb'd axle assembly offline for probably too much money but swapped it in and it works.... cheaper than having a shop rebuild my diff.