Low Rumble in High Gears

ARrado15

Hey all. So i've noticed over the past few months that while in 4th and 6th gear at around 3k rpms, I start getting this low rumble noise. To be exact, 4th gear does it at around 3200, and 6th at 3k. Its so hard to explain, because i've never experienced it before. It does not do it while accelerating/decelerating through 3k. Only when i'm crusing at/around 3k rpms. I also find it odd how when i downshift to 5th gear, I do not hear the rumble. Also, 1st-3rd do not make the noise no matter the rpm. I can feel it in the steering wheel (though only slightly) and the pedals. For some reason though, my passengers are oblivious to it. It's just really bothering me and I would like to get to the bottom of it.