Roaring sound when accelerating only

[Yella_dog]

1998 Expy XLT 4WD
When I get to about 25 mph there is a roaring noise coming from either the differential or the rear end. It only does it when accelerating and if I left off the gas it stops. Has anyone heard of this and if so where should I begin diagnosing the problem. When I am driving it is hard to tell if it is coming from the front or rear. IMy job requires me to travel and I don't want to be stranded on the interstate somewhere, nor do I want to have to pay $2000 to rebuild trans. Thanks. JT

[RickMN]

Go on ebay and shop for a used Steelman Chassis Ear set. They're a set of 6 clip-on microphones. You attach them to various suspected parts and run the wires into the cab. Drive the vehicle with headphones on and switch from one mic to another. That will nail the problem every time. Steelman came out with a wireless model last year so lots of shops are selling off their old wired models on ebay. You should be able to pick up a set for about $75. That beats the heck out of guessing and is less than 1 hour of diagnostic time at shop rates. Plus, it's a great tool to own. I don't use mine often, but when I do, it's worth its weight in gold.