Hey, all. My 2004 road hog has a loud whine that increases with speed and mostly goes away when coasting. It's hard to identify where it's coming from, but it sounds like it's under or behind me. It seems to reverberate through the whole truck.
The transmission fluid is where it should be and is very clean-looking with no burnt smell. It also shifts smooth as butter, even when you're hammering the bitch. I can't feel any real play in the driveshaft. My first thought was the rear diff, so I pulled the cover and inspected it. Everything looks normal. There was a little bit of goop on the magnet, but far from the worst I've seen. I refilled it and took it for a ride the next day, but there was no change it the sound at all, even with new oil.
I pulled the transfer shaft off to rule out transfer case issues, but no noticeable sound change or feeling. I drained and refilled the front diff oil, and it's the same deal. No change and no obvious issues. The oil was clean and had minimal on the magnets. I'm not sure if there are any parts of the transfer case that would still spin while in 2wd and with the shaft from the front diff removed, but I can freely spin the output end from the transfer case, so there shouldn't be anything connected.
Can't feel any real heat in the hubs or cvs after driving, either. I do plan on changing the front hubs and cvs, anyway, since there's the tell-tale light clunk on occasion when I've got the wheel cranked, but it's barely noticeable. No play on the wheels, either.
The former owner said it's always made that noise and he has no idea what it is, but I think he's full of shit. I have no way of contacting him now, though. I have a receipt from when he had the engine and transmission swapped a couple of years ago. The engine and tranny they put in had around 75k miles on them and were put in about a year before I bought the truck. If swapping the transmission didn't get rid of the noise, I doubt it's anything to do with that. They also put a new driveline on.
So I'm kind of stumped. Is there a particular bearing I should be looking at in the drivetrain somewhere? It's such an annoying sound, but it doesn't seem to affect how it drives. Is this a diff gremlin that can only be sorted by tearing it down and rebuilding it?
Any input or suggestions are appreciated. Thanks, all.