Been hearing a on and off humming noise from the passenger side a couple of times. First time I heard it was about a month ago and now today. Not sure if it's a bad wheel bearing or not. What do you guys think?
Today I heard it on and off for about a mile - almost sounds like an aggressive mt tire on the freeway.

Sounds like a hub bearing to me. I've had to replace both sides on my 05 4runner at different times. When I was troubleshooting mine I noticed that the sound would intensify and fade away as I rocked the wheel left and right going down the road taking the pressure on and off of the bad hub bearing.

A bad wheel bearing is not difficult to identify. It will sound like a low pitched droning sound (like a propeller) and will get louder with ONLY speed, regardless of the engine RPM. So, get on the freeway and put your rig in neutral. If you still hear a "low pitched drone" sound while rolling in neutral, the odds are pretty good, that your bearing is bad. Take it home, put your Runner on a jack so the affected wheel is in the air; then grab it and push/pull. If there is any give, you definitely have a bad bearing. Good luck!

Ah thanks guys.

Search for "rumble strip" noise in this forum. Is that what you are hearing?

What type of tire are you running? My Coopers before I replaced them were always off and on with a humming noise. I thought it was a wheel bearing as well, but when I swapped the tires everything was good.

There are probably multiple ways to diagnose bad hub bearings. You should hear a humming noise going straight. In a curve at high speed as you turn the wheel in one direction the humming noise should go. If turning right and the humming noise goes away, you have a bad left hub bearing. This is due to less load on the left hub as you turn right. Same applies in for the right hub. The second and sure way to diagnose a bad hub bearing is to jack up both front tires off the ground. Grab the 3 & 9 o'clock positions of one tire and rock the tire back and forth to see if there's play in the tire. Also grab the 6 & 12 o'clock position of the tire and rock the tire and check for play. If there's any play while you move the tires, you have a bad hub bearing. I use this method to determine a bad hub bearing on my 05 4Runner. Although only one is bad I end up replacing both. I bought pre-assembled hub bearings from some one on this forum. It costs $170 shipped for each side.

I respectfully disagree with part of what you said. I've seen/heard bearings begin going bad with the only audible noise occurring when turning one direction or the other depending on which side the bad bearing is located, and yet, be very silent when traveling straight. Go figure.

I think it all depends on how the hub bearing is failing and there are probably more ways to detect the problem. In my case and a lot of other cases, the humming goes away in a turn. During a turn the force is distributed more toward the side that's turning and therefore the humming goes away if the bad bearing is on the side away from the turn. It's quite possible to hear the humming noise only in a turn. As I said in my post, a better way to detect the bad hub bearing is to check for free play with the tires off the ground.