I have the same noise when pulling 5th wheel weighing 13,800 lbs. Had repair shop test with 5th wheel hooked up. Was told exhaust leak was the problem. Cab was removed and all gaskets and down pipe was replaced. Hooked up 5th wheel same problem after $2500.00. They removed the cab again and pulled turbo off and someone who rebuilds turbo checked them and said they were ok. Was told it must be the transmission, had transmission shop check transmission and was told it was ok. Still have same problem. I have only heard of this problem on job 1 trucks!
If anyone has the answer please let me know.
I think its the tranny shift program, I did a relearn on the tranny and fixed the majority of the noise, now the noise starts when the rev limiter starts dropping cylinders. so my feeling was somthing in the computer controlled valve body or lockup on torqe converter, havent tested with fifth wheel yet. but a world better already
Just a random thought,!?! ... about a year and a half ago i took the truck in to have the batteries checked, and both were replaced. did the tech remove both at same time? hum? probably been riding with ill-programmed tranny since!
I hope that takes care of your problem. My tranny has been reprogrammed 4 times and has not helped. The noise can only be heard when I am towing my 5th wheel. I can not make it happen when the truck is empty.
I tried to duplicate the sound this past weekend with the 5th wheel hooked up but couldn't. Today I had a car trailer to haul, and after dropping it off tow haul wouldn't disengage at hwy speed, and the sound came back. I'm thinking the transmission might need to be re-programmed, and that might solve the problem. Just a guess at this point.