The old transmissions and rear ends had some whine to them, but if it's excessive, the oil may be low or worn out. Might change it out with a heavier weight and get by for a while.
oil has been flushed, new clean 90wt, opened and no indications of wear, no metal particles in old oil, have 2 and both have gear whine, low not excessive yet
My 53 chevy had a pretty loud whine. I changed my oil out too and made no difference and it only had 85000 original miles. I enjoyed the whine after i realized there was nothing wrong.