Well...if I had to guess, it sounds like you are missing a tooth/spline in your diff.... But, it could be trans too. Do you have access to a hoist? If so, lift the wheels off the ground, put it in gear and then raise it so you can hear/see where it's coming from at this point... Definitely something rotating with speed. It could be anything from bearings in the rear wheels all the way to the front of the trans. But, since it doesn't get louder with speed and stays consistent with speed, I'm willing to guess you chipped a tooth.
Solo Street Race exhaust
ASAP T2 stripes and badging
Windrestrictor V2 lighted in white
Windrestrictor lighted door sills lighted in white
DDM Works IC Piping
Undercar LEDs in white to match Windrestrictor
ZZPerformance dyno tuned - 286HP, 317ft/lbs of torque at 23psi of boost.