weird sound coming from rear end!!!

[Stedman05]

I have a friend with a 84 rx7 and something just messed up on it. He came to a stop light, and when the light turned green, he punched it. He didn't spin the tires but suddenly he heard a really loud grinding sound coming from the rear end. The sound has died down some but it is still there. It now sounds like a supercharger whine. You can only hear it when he is accelerating. What do you think could be a problem?
Thanks

[WV85RX7]

Troubleshooting noises, grinds and the like can be a bitch. Could be a driveshaft flange, differential bearing, rear wheel bearing etc..
Does he have a GSL or GSL-SE model? Both models came equipped with LSD rear-ends.. I would hunch that if the noise just started after a hard launch- check the driveline flange (u-joint) first, then the wheel bearings, then the differential. Here's a nice guide too:

http://www.mazdatrix.com/g2.htm

[Stedman05]

My friend figured it out. He ran it out of gear oil.

[WV85RX7]

Hmm.. They rarely run dry. Tell him to put redline in there. His rear end will love him for it. Do the same with the tranny (if it's a standard).