Tacoma making a humming noise

If there is warranty, I'd take it to the dealer. If not, I'd start with tires, check for cupping and rotate. Then I'd check the driveshaft and make sure u joints are good and/or greased if applicable. Then change the oil in the diff, just in case and see what condition oil drains out.
Also, I'd see if any weight in bed changes the noise, if it does then it's not the diff and probably driveline issue.

 

I was gonna say wheel bearing. I had a front one go at 90k miles. Same thing, humming noise at 50mph+