changed gears in a 741 now have a whine

Is this a Sure-Grip, or open? Could the spider gears be causing the problem? I don't see how they could since they are turning with the carrier, and the side gears, without any relative rotation themselves when going in a straight line. Just mentioning it because I have a diff that feels fine when both tires are rotated back and forth, but if one is held from turning, the other one can be rotated about 45° back and forth.