You can try changing the oil, can't hurt. I would step it up to the heavier viscosity, the Lucas 85/140 is a good oil. Unlike an engine, with gears you don't need/want to go fancy with synthetics. If the noise goes away, either the old oil was severely broken down, or the thicker stuff is masking an imminent problem. If nothing else, going inside to change the oil gives you the opportunity to explore.

 

69 has good points, and I would follow those. That does sound like the gears though.

Worst case though, as Craby said, just need new gears/bearings.
If you're going to re-build, do what I did with my destroyed rear end and get some 3.42 gears! Definitely hurts gas mileage, which I don't mind as mine is a weekend fun car.
I have another vehicle for daily drives. If this is your primary car, I would maybe look at only stepping up a hair, maybe 2.73 or 3.23. Either way, gas mileage will go down as you go up.

 

OK thanks, I will try the thicker oil and see what happens!

 

Also, should I add the limited slip additive? I am pretty sure this is not a LS diff.

 

I would say you don't need it, but from this thread I found here (different forum), it seems like it can cause your oil to break down faster if some additives are used.

Seems like a lot of diff oils are pre-mixed with additive, and it seems best to avoid it if you don't need it, but the fluid won't hurt your parts from what I'm reading if it's already there.

 

The additive is for clutch type limited slips. Even if your (2002) car had l.s., it would be the Torsen (non clutch) style, which replaced the clutch type in the 1999 model year. An additive would be a waste of money.

 

well my 95 requires .so many ounces of of limited slip addative with each change ,my guess.is he does not need it because no posi

 

Read what I put above. Even if his has a posi, it doesn't need the additive.

 

well I am just saying what my hand book says 4 ounces of gm 1052358 an both guys who have worked on mine said it was needed for my car his well ,he should see what his hand book recommends I seen what you said .but when something comes.highly recommended bye 2 master mechs an my hand book I do it ,so he should check his hand book .using heavey gear oil is only temp for most,i just happen to be doing mine soon changing the gear oil an yes even for my .auto trans too,the book does not say manual it just says limited slip rearend needs it .?so why do you say it does not need it ,is it couse its on its way out the heavy gear oil..,oh an god knows my rearend has took a pounding but I have changed it every 5 years too ,an still working pretty good under all that new power.i just ordered 4 ounces of it for mine,now for no limited slip no additive needed is what the book says .that must be your personal experience ,as I was told not using 1052358 can couse damage to any limited slip gear box .

 

Your handbook says to use the additive because your year still has the clutch type posi. The reason for the additive is to prevent the clutches from getting gummy, sticking, and making the rearend go clunk clunk clunk around a turn.
1999-2002 has a Torsen (Zexel/Torsen) lsd, which do not have clutches to get stuck, it's totally different. Comparing his to yours, you might as well be comparing what a Toyota has vs what his Firebird has. His V6 Firebird will have limited slip, if it has the Y87 package.