[ins0mnia24]

Sounds like the driveshaft. does the noise get faster as you drive faster?? is your car a A4 or M6?? or it could be your Universal joint. either put your car on some ramps or put it on a lift and check all your driveline nuts and bolts to see if any of them are loose, then maybe check your rear differential fluid. on the rear housing you will see a fill/level check plug i think its a 3/8 fitting then take that out and see if the fluid in your rear is at the top of the hole or if some drips out, your rea fluid should be even or a little above the hole then some will drip out when you take the fill plug out. shine a flashlight and make sure your fluid is filled up to the hole if not then it is low, then you just go get some fluid and use syringe or funnel and fill it until it is at the bottom of your fill hole