Truck sitting for a few years

Easiest thing to look at and rule out is tire wear and pressure. Besides that, there might be a shock that's gone out, or something else.

 

I really do not recommend purchasing a truck that sat that long. There will always be open valves in the cylinder head that will allow dampness to get in. Over that much time you will get rust forming inside the engine. It may clean off, and may no. Same thing goes for gears in the trans and diffs. Anything submerged in oil will be fine, but any gears or bearings above the oil level will eventually start to rust. How much, and how much damaged actually occurs is up to mother nature and father time. 4 years is a long time. 1 or 2 years even I would not be worried, but 4 is a long time! Parts need to keep moving and actuating to stay in good shape. I would suspect the vibration is from a dry ujoint, or sticking slip joint. Hopefully that's all it is.

 

I would plan on replacing or at least having the tires checked and rebalanced. That vibration may be a tire which the belts have slipped or just ruined by sitting too long.

 

Front wheel bearings for sure.

 

After four years sitting in one spot can't be good for the tires, dry rot and probably out of round will cause a vibration but not the noise, could be two different problems.
Axle seals will be the first to go, then the through shaft seals.
I purchased a dump truck that sat for over 2 years and one of the first problems i had was to get the grease to move the rust and crud through the s cams and slack adjusters so they worked properly, i replaced the U joints because they wouldn't completely take the grease and replaced the carrier bearing because of dry rot.

 

He says the truck has been sitting in his yard so I take it he already owns it and isn't buying it, but still all good advise Heavyd. I'd check air pressure for sure, but after sitting so long I know the tires have flat spotted but should round back out after driving it a few miles. I'd also replace all belts and water hoses and then I'd run it around local for a few weeks just to be sure everything is OK.

 

At 50mph, I would think a tire would cause more of a shake than a vibration.? Perhaps some rust spots on the brake drums can cause some vibrations? If you can tell us what engine perhaps the noise can be from the turbo control components and/or a leaky charge air hose that rotted?

In general, I think the air bags should be inspected or replaced. The coolant should be tested and if needed replaced. If it were mine, I would replace the brake pots and cans. Maybe look into the air dryer and replace the desiccant?

 

As puncher said, i would stay close to home for alil while. After sitting that long, i am sure you will be doing some repairs. Hopefully, they will be small,
"inexpensive" repairs?