It started when I was driving down the highway at 70-75. I slowed down for construction to about 50 and that's when I started hearing the strange two sounds. After the construction, I drove back up to 70 and the noise stopped. But as soon as the speed dropped below 70, the noise started back up again. It definitely got louder as I came into town and slowed down. The noises would continue at any speed, but would stop when I do. Turning the wheel did not affect sound.
The first, and loudest sound I noticed, sounds almost like a wheel bearing, but a lot worse. I would describe it as the sound of a motor bike. The second sound sounded kind of like faint metal rubbing, but it's definitely not as loud as when I came home.

 

My first suggestion would be to get underneath and look for anything obviously damaged or lose.

 

Also check the rear drive shaft and, if AWD, the front drive shaft.

 

I did forget to mention that it is a 4x4. The loud noise happens in the front and is louder when it is on the ground, but you can still hear it when it is lifted.

 

I'd check the brakes and wheel bearings for excessive wear, play, and/or noise while turning the wheels by hand (have someone lightly apply the brakes while you turn the wheels). A cracked rotor can cause what you're describing (this is pretty rare tho).

Another, more likely issue, could be the locking hubs, no, make that the CV joints (the front diff has an internal locking mechanism). Btw, how many miles are on it and, how rough are the roads and highways in your area? And do they salt and or sand the roads due to weather?

Post edited due to slipping mind.

 

Get the front up and place jack stands under the lower control arms so that the front half shafts are level. Turn one tire/wheel and see if you can isolate the noise to one side or other.
Could be as simple as one of the front backing plates got bent somehow and is hitting the rotor. Check caliper bolts, brake pads, etc, etc. Could be the front diff locking collar is partially engaged. Could be one of the half shaft CV joints has failed. Also check front driveshaft as it has a CV joint at the transfer case.

Let us know what you find or do not find.

Good luck.

 

There are 151k miles on it. The roads aren't that bad around here, but I do drive many places and every once in while I hit a pothole. And I live in MN so yes, they definitely salt the roads during winter here.

 

Does it speed up and slow down with acceleration

 

The sound on the highway did not change much if I gunned it, so I don't think it's anything to do with the engine. Otherwise, yes. If I described a motorbike sound as 'bababababa' (which what it sounded like at 60 something) when I had to stop at a light, I could definitely tell it slowed to 'ba ba ba ba ba'.

 

Good news! The problem has now been fixed. It was the 4WD Actuator in the front diff. It was mechanical and the wire was rusted causing the diff to not fully disengage.