I've got a new 2500HD. Drove it back East to pick up a fifth wheel and encountered a strange sound, usually when towing up a long steep grade. About 2000 or 2100 rpm, the vehicle sounded like it was downshifting, but the rpm's did not change. The sound would continue until after most of the uphill load was gone. Is this a normal occurrence? Is it the turbo that I am hearing, or something in the transmission?


Thanks,Edited by: Rollin' Thunder

Sounds like the turbo to me bud.

Hmm...


Towing up a long steep grade? Sounds like the engine fan clutch engaging to me.


At a certain engine temp, the fan will engage to keep the temps in the proper range. Makes quite a bit more noise than usual and on first notice, seems like maybe the engine downshifted.

.....ahhhh....fan clutch sounds like the logical answer. That would also explain why the noise didn't go away immediately after cresting the top of the grade. Thanks.

fan clutch is what it is. They sometimes kick on first thing in the morning too.