I'll keep it short and simple. At 60 I get a very low pitched droning sound coming from the back of the jeep. I believe it's probably my ujoints. It's 2wd so I only have the rear shaft. When I did my brakes a couple months back I shook the tires and there were as tight as could be so I don't think it's wheel bearing. Maybe differential but the fluid was of normal coloration, and gears looked perfect. 215,000 miles. Goes away when I get above 70mph.
Hmm, we'll the tires are brand new. It did it before I got the new tires also, so I'd hope the tire shop would get the balancing right, especially since they are a reputable one. Interesting though with the exhaust. Maybe, I do remember seeing the exhaust coming out a seam of the muffler one cold winter morning. I would think it would drone all the time. Sometimes it sounds like its oscillating, if that makes sense. It's pretty loud, and always starts at 60. I've never experienced bad ujoints before so I'm not sure. My last jeep had a bad pinion bearing. This is definitely a different noise.
Thanks for that suggestion guys! That was a really good idea. I ran it in 2nd gear, also took off OD. It happens around 1800-1900 when at 60-68ish. But at the same rpm in 2nd (about 25mph) and in 3rd (about 35mph) it was pretty normal and quiet. I definitely think its speed related and not rpm.