I have a 2015 unlimited Rubicon with a 4.5" lift and long arms from Synergy. I am getting a vibration/groan from about 65 mph up when cruising on the highway. It does have mud tires but to me it sounds like something other than tire noise. It is low sound and vibration that goes for about 2 seconds then its fine for 3 seconds. Constantly in this pattern. It also seems to start kind of low by my feet then vibrate through the vehicle getting louder. Any ideas of what to check?
Thank you!

 

maybe driveshafts? 4.5 inch of lift is a lot for stock driveshafts and joints

 

Driveshaft would be an easy first thing to diagnose, especially if you are feeling like its right by your feet in the driver foot well. Check to see if the U-Joint on the flange going to the front differential has any slop in it.