Hello, All!

My wife recently started hearing a humming noise while driving back and forth on her daily commute.

She said it was humming, to which I asked: "But can it carry a tune?"
(that's when the fight started)

It doesn't seem to be the normal humming one might expect from unevenly worn tires, etc. The tires are relatively new and I just had them rotated and balanced a month ago. I have ruled out wheel bearings which has me thinking it could possibly be from the rear differential.

Before I crawl up underneath it to check, I'd like a second opinion. I'm handicapped, getting down is easy - getting back up is another story.

need more details. is it all the time, when the truck is moving, when applying gas only or just moving? etc. if you've eliminated the front end from possibilities and it is in fact coming from the rear you have really only the transmission, drive shaft, differential or rear wheels. depending on the specifics of your situation you may be able to rule out a couple options

when is the last time the transmission and differential fluid was changed

Thank you for the response!
The sound is definitely coming from the rear of the vehicle and is only when the truck is moving. The hum also does seem to correlate to the speed of vehicle and is louder at highway speeds.

There is no noticeable vibration and it doesn't sound like normal tire whine. It sounds somewhat like a tire rubbing on the plastic fender well splash guard but that would be more obvious. I've also considered the possibility that it may be exhaust related.

I plan on checking the transmission fluid level, belts, pulley's first, once I get it pulled in the garage this evening.
No CEL has coded, but will check things out via the OB2 just in case.

I am the second owner, and although the vehicle was meticulously cared for I didn't get the service records from the previous owner. I did, however, take it in to Toyota before purchasing, and had them check it from top to bottom with no deficiencies noted. I should probably get it in for a drivetrain service just to be on the safe side.

Thanks again!

Just a quick update!

I found the cause of the humming noise. (Front D/S "Bad" Wheel Bearing)

Problem solved!