I’m a complete novice on auto repair, so forgive my ignorance. My 2012 F250 has begun making a noise. The noise is coming from somewhere in the linkage (drivetrain). It sounds like new knobby tires on a paved road but not constant more like (rrrr-rrrr-rrrr). The frequency of the noise increases the faster the vehicle moves. It does not make the sound while reving the engine in park and the noise does not change between dirt road of paved road, so I’m pretty sure it’s not the tires or the engine. Could it be something like the tachometer needing lubricant??? Its kind of loud. Thanks for any help.
What engine, transmission?
Does the noise change if you drive at, say, 30 MPH in different gears?
Linkage it is not but a drivetrain noise. I would check the level of the rear end fluid and maybe evan change it out.
This rear end may require a fluid with a friction modifier and you can look that up in the owners manual. If no manual…you can call any Ford dealer and they can tell you. Be sure to go with a quality fluid that matches the factory spec’s. If you cheap out you may still have the noise with the new fluid.
Yosemite
If this sound stays more or less the same in drive vs coasting at the same speed, you’re probably looking at the drive shaft u-joints or splined-joint if you have a two part driveshaft, or one of the differentials. rr rr rrr sounds can be caused by a faulty wheel bearing too.
If my own Ford truck had this problem, I’d lube the driveshaft u joints and splined-connection, and check the differential fluids as the first course. Next would be to check the wheel bearings by jacking the wheel off the ground and spinning it by hand, making sure it spins freely, & listening for weird noises. Then grab hold at 12 and 6 o’clock, both twisting and pulling, checking for excessive play.
It does sound like a drive shaft or rear axle problem as mentioned already. And BTW, automotive tachometers haven’t needed lubrication since the 1950s when cars were real machines that kept men busy many afternoons and most weekends. MIarriages may have lasted longer back then thanks to the automobiles need for attention.
Are you implying that cars are no longer real machines?
Come work with me for a week
You will change your tune, REAL fast 
It makes the same sound uphill, flat or coasting downhill. 2wd or 4wd. Any gear. Many thanks.
Thanks to all who took the time to respond. It turns out both front wheel bearings need replaced. Dealer will do it under warranty, only 46,000 miles on it. Odd thing is my local mechanic had a hard time diagnosing, because the wheels did not have any play in them when tested in the usual way. I wonder if using it to plow snow could be that hard on the bearings? I bought it used, back in Jan. 2014, previous owner would have gone through the winter of 12/13 with a plow, he may have been commercial. I only used it maybe 25 times to plow my driveway the last two winters.
Thanks for closing the loop and adding to our collective database.
Yes, plowing is hard on a vehicle.
There’s nothing odd about it
If a wheel bearing is rough, but doesn’t have any play, it’s bad and needs to be replaced
I don’t have any stake in the company, but I’ll say it . . . chassis ears would have helped diagnose the cause of the noise
In fact, I’ve used them myself a few times, to diagnose bad wheel bearings. Which had no play, but were rough, BTW
It may have absolutely nothing to do with snow, salt, water, etc.
Thanks for posting back OP, good info. As posted above a wheel bearing can be kaput without showing any excessive play. A bad one will still usually have a grinding or raspy sound when hand turning the wheel.
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I agree.
Another old trick with wheel bearings is removing the wheels and turning the hub by hand. The mass of the wheel and tire can mask a rough bearing by acting as a damper.
Like the others, I sincerely thank you for the follow up post. It’s good to hear of successes. 
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I agree it is nice to hear back from an OP, and to learn what the cause of a problem was
All those times, when somebody reopens an ancient thread and says “I’ve got the same car and the identical problem. What was the solution?” I think that the car probably was fixed at some point, and it would have been nice to know what the underlying cause was. There’s a lot of things to be learned on this website, IMO