Have a 99 F-350 4x4 dooly. Once a week I will hit a bump or rough spot on the hwy and I will get a high pich---almost a roar from under the truck (it sounds like it is on the drivers side---but that is the side I am on). It sometimes will last a little ways and sometimes it goes away quickly. One time I slowed down and tried to get off the side of the road and almost got to a complete stop befor the noise stoped. The brakes nor your speed seems to have an effect on the sound. My Mechanic has had the truck for three days and has only been able to get it to make the sound one time, he has another 99 F-250 4x4 in his shop right now for the same noise. He has called Ford and researched the internet with no success-------ANY IDEAS

Thanks Rodney 770-914-8935 WK

 

shot in the dark... maybe look at the carrier bearing (between the two drive shafts going to the rear)

 

i wonder if thefan clutch is acting up and when you hit a bump it engages the fan clutch??????

does it affect performance? any vibration? if it was a carrier bearing it should be vibrating. does it get quieter as the engine rpms go lower?

 

I'll toss out another... I'm really reaching here, but, if there is crap in the bottom of you differential and you hit a bump causing it to move, you may hear a growling sound... it happened in my wifes durango (I hate to even mention a D@d&# product here, but she had to have it) her daddy is a mechanic so she took it to him... he drained the diff, put it back together, no more noise... I know its a LOOOONNG shot

 

There is no viberation, there is no loss in performance and the carrier bearing seems to be fine. The noise does not appear to be coming from the rear of the truck but we will check the rear end. The sound is kind-of like when you run off the road in an area where they have put the grooves in the asphalt to let you know you are off the road but magnified greatly. The noise appears to be triggered by a slight bump of some kind----change in asphalt or of the like. The transmission in new but someone mentioned maybe the torque converter is a likly source.

Thanks Rodney