Strap someone underneath with a stethoscope while you back up!
Well, sure, there might be safer ways to find the noise. One way is to jack up the rear axle and run it in reverse to see if it still makes the noise. If only one wheel turns, it will be normal to hear gear noise from the differential. If you have a locking differential, it should be quiet until you turn while backing up. Even then, at such low speeds, it shouldn't make much noise.
Look at the tail pipe moving when the engine rocks when placed in reverse. Perhaps the muffler is rubbing on the drive shaft. If you still haven't figured it out, mechanics have a tool called a chassis ear. It's 6 microphones clipped onto suspect locations. You drive with a receiver, and switch between the microphones, listening for the loudest one. By moving the mics around, you can zero in on the source of the noise.
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Sunday, November 29th, 2009 AT 11:52 PM