After fixing my engine problems(dead cylinder) I decided to go out today and ride around for a while. After driving fairly hard for about 30 minutes I started getting a whirring noise coming from the rear while going over 25 mph or so. Any ideas of what to look for? The front of the differential does look like there is a fluid leak.
1989 Formula 9 bolt with 3.27 gears

 

Change your u-joints before diving into the rear.

If it turns out it's the rear, it probably needs pinion bearings. Since you have to COMPLETELY disassemble it to change those, might as well put the others in it too; carrier, and axle. Plus of course the seals.

 

U joint is my hope if I am lucky. I am going to take it to a shop tomorrow and find out what it is. Bad thing is if it is the rear they will push a Jasper over going too much into it and I am not going to spend that much on the car.

 

Rear is toast. Got a line on a used one. What should I go ahead and replace on it before I have it put on the car? Bearings? Seals? Or just leave it alone?