I have a Silverado 2500HD crew and a CST 6" lift with 35" tires installed after 5000 miles. I now have 52,000 on her. Never had any issues with the 4wd system until I was in heavy rain a couple months ago traveling about 40mph and switched in to 4 high. I heard a terrible roaring sound and vibration.

I don't use 4wd much, maybe 5 times for short periods off road and a few wet road launches about a year ago. I don't beat this thing up, she's a pavement princess.

I took it to the dealer to have it checked out while in Jonesboro, Ga and they said it was the driveshaft angle without doing anything but driving it down the road. Well, the lift has been on for 45,000 miles and never had this happen before. Don't take modified vehicles to Terry Cullen Chevrolet. They have been instructed by the owner to just blame it on the mods and send you on your way. (the owner told me about this himself)

I checked my service records to find it was time to change fluids in the front axle and the transfer case. I had the front axle fluid changed and still vibrating and roaring. Next I'll change the transfer case oil.

Anybody had this type of vibration or roaring sound?:help:

Is your front pinion angle changed any from stock? Because I know if you don't fill the front diff through the diff vent the pinion bearing will not get lubricated on the Cognito 7to9inch lift.

It had to change some for a 6" lift. I just had the fluid changed, but the dealer may not have thought about the changed angle and the damage is probably already done.

Yep that sucks I heard this happen more then once good luck!

Any more ideas?:confused:

The pinion angle looks pretty much like stock. This is only a 6" lift.

I don't have a lift but have similar roar in 4wd,
were you able to resolve the issue? pls share...

Not figured out, yet. Been too busy to deal with it. GM voided my warranty without knowing what is causing. I'll keep you posted.