I have had to resort to a friend partially hanging out windows on occasion to locate the source or at least suspect area of the noise in some cases. Make sure to use a deserted road. You might want to check to make sure the rubber mount around your centre bearing is still pretty intact as well as each rubber disk at both ends of driveshaft. The rubber disks are important to find if going bad. Could just be a tire with a problem too. But only when accelerating when cold kind of eliminates that. Another thought is a constant velocity joint on the rear axel might be on it's way out. Examine your rubber boots on the rear axel for tears or leaks.. For diagnosing that if there are no leaks perhaps get a friend with quite a bit of automotive experience to ride along. Just do a quick check to make sure all your lug bolts on the wheels are snug as well. A lot depends on the frequency of the noise and of course intensity. Noises sometimes are easily found but not always. Other than what I have mentioned nothing particular comes to mind. Wait and see what other sugggestions are posted. These things can be hard without actually hearing them. Even then sometimes they are still interesting. I suspect you will find the source of that noise by the way and let us know what it was.