Odd noise after a load of firewood?

So I have a 17 sr 4x4 2.7l with 3k miles on it now. As the title states i have developed a noise. I'm not sure if it was there all along or not, but I didn't notice it until after I hauled a load of wood for about 10 miles. It also has gotten cold recently.
Now for the fun part, let's try to describe the noise. It is more of a vibration i guess, mind you not a shake it shimmy like a tire. It has been a couple hundred miles since I noticed it. At first it was very hard to duplicate, but now it seems to be getting more pronounced. It happens between 45 and 50 then it will go away. No more noticeable than bass from a speaker shaking the floor. It's a repetitious sound but too much time between for it to be keeping up with tire speed. I read about lifted trucks having a needle bearing in the front diff that has a similar description. I don't feel it in the steering. It's the same as engine vibration at low rpm but has a definite harmonic pattern to it.
I am an auto tech by trade and this one is interesting, if I had to guess what it sounds close to it would be a bad wheel bearing but can't make the sound change and it's too slow.
I suppose just point me to any other threads about vibrations other than the front bearing i mentioned
Thank you

 

I had a noise that I couldn’t pin point for weeks similar to what you are describing, ended up being wheel bearing

 

Could be the infamous Rear Diff Howling that you are noticing, it is a Harmonic sound roughly in the 50 - 60 mph range while feathering the throttle