Loud low drone noise at speed

My very reliable 2001 SR5 started making a low frequency drone above 60ish. Although I have heard it sometimes 40 - 50mph, it is usually at higher speeds. I threw it in N on the Highway to see if it was the engine,,,, noise did not change, I rev'ed the engine, smooth as always, . Not sure if that actually eliminates Tranny, but I am thinking maybe a wheel bearing? Never had one go bad on a vehicle before, so I am unsure. or maybe Suspension item?
It shifts fine and all accessories work.
I checked the tires for bulging and they are good.
Difficult to diagnose since it happens at high speed.
No codes either.

Any ideas?

Thanks,
ED

 

Could be. The wheel bearings are really beefy on these but they will go bad some day. They do start to make noise in the lower frequencies.

If you put it in Neutral and the sound doesn't change, it's probably not going to be the transmission. Could be the rear diff or u-joints or drive shaft.

https://www.youtube.com/watch?v=UpsLaSzcAu4

 

Thanks, for the reply,,, You just reminded me that about a year ago I was getting a squeaking sound when in reverse, Looked it up and pointed to possible u-joint,,, the sound went away, but this might be it resurfacing.... I'll look into diagnosing and respond for anyone else.

Thanks,

 

Sounds like wheel bearings…
Just did mine a couple thousand miles ago
They’re not to bad to do… plenty of videos on how to do it

 

I am thinking that too as a possibility. Thought it could be the motor or transmission mount, but they both seem to check out.
Thanks,

 

I get what I think you’re referring to, but only sometimes when going downhill and only at highway speeds. Never just cruising on a flat highway. Changing speed or coasting doesn’t matter. Wheel bearing as well? Can’t be the U joints I just had those done a month or two back.

 

You can jack the car up and check for free play on each wheel. Basically hold each wheel, say top and bottom, and see how much play there is. There should be a tiny amount at worst. Perhaps in this case the one with the bad bearing may show more play. The other possibility with older cars is the rear differential. As the gears wear out, one starts hearing humming noise.

 

I put it up on jacks last weekend, With rear wheels free I had the vibration, So I removed tires to eliminate any mis-balance and still had vibration. No noise from rear either, so kind of discounting wheel bearings.
The driveshaft "looked" fine, didn't seem to show any unusual movement between 30mph and 65mph, range where vibration typically begins.
The engine runs smooth when in park or neutral and revved. I am thinking tranny could be going? I checked the tranny mount and it didn't have play, did the motor mount test and the engine did not move with brake on and giving a little gas in forward or reverse.
The mystery continues...

Solved -- Very easy to remove drive shaft, 4 bolts at the rear axle. Once I removed the drive shaft I could see that the front U-Joint was shot, I had also noticed some grease splattering on the underbody, and that is what led me to believe it was the u-joint.I couldn't verify it was bad till I removed the drive shaft and was able to inspect the front u-joint. 30 minutes later new drive shaft installed and 4Runner is smooth again.
The I found the torque spec for the 4 rear bolts 54 ft-lbs.