1988 Other Chevrolet Models differential is whining

There can be a coule of things that cause this. One it can be the pinion bearings may be to tight, but that might also whine all the time. The gear depth may be not deep enough, especially ifyou changed ratios and used the same shim. Or the backlash is wrong. If you clean the gear with fluid, and put paint on it, you can turn the gears to see what the pattern is. It should be as close tothe center of the gear as possible.