Gen 3 vibration

[CrispyCracker]

Been a while since I posted. Bought a 2001 Gen 3 XLS from a guy up the state last year and went to work on maintenance items and then added some basic equipment and fun mods (bash plates, 32" KO2s, -12mm offset wheels, etc.) Took the family on a road trip from Florida to Carolina and she did very well. KO2s hummed some but after a local shop resolved a wheel balance issue she tracked straight and road noise was acceptable.

Here's the problem: over the last six months or so the truck has developed a crazy loud hum/vibration -- seemingly from the drivetrain -- that shows up around 30 mph and gets crazy noisy from 40-60 mph or so. I'm talking loud. Now, I'd suspect that the tires were an issue but they're still relatively new and were not a noise issue for months. I changed the rear end (hybrid diff) fluid with Mitsu-recommended stuff and local mechanic says rear end seems fine. He suspected driveshaft (we were both surprised to learn that it's made from composite material) but now is not so sure. I removed the rear dampening block (per recommendations on Aussie forums) but it did little to help so I plan to reinstall. I asked some folks on a FaceBook forum and several posters recommended rear bushings so that may be my next move -- but it seems odd to me that worn bushings could cause such a racket. Anyhoo, I'm back in this joint because I've received great advice in the past from the assembled gurus.

What is the first thing you'd suspect here? All advice/input appreciated. Sadly, the noise factor is taking the shine off an otherwise great truck.

 

[Tjtalan]

I would start with a thorough check of the wheel bearing.


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[Inyo_man]

I would begin by completing a transmission fluid flush (9-12 quarts), and replace the transmission fluid filter.
The transmission can shudder and such if the fluid is old, or something other than Mitsubishi Motors Fluid was used.
...besides, it's general service.

Cheers

 

[Salonika]

When it is happening, how does the sound change if you weave back and forth?

 

[southofantarctica]

Have you tried a tire rotation? I know you said that it shouldn't be that, but I was dealing with a similar situation a couple months back and it ended up being due to uneven tire wear. Like bad. Just started up on day out of the blue.

Also, that dark grey cladding looks super sharp, what did you paint it with?

 

[Unchboy]

Is it only under load that its making the noise?