Yes and no...You did not mention what they are in. Generally, you should not hear the gears in a loaded condition unless you are climbing a hill on the highway or are hauling a heavy load. Actually the same holds true for deceleration, but this is where you may hear a very small amount of noise even with a proper set up. Most 4 wheel drives generate more noise out of the transfer case than the differentials, especially all-gear (no chain) cases like an NP205. If you can hear your gears under normal driving conditions AND you are sure it's from your differential(s), you should have it checked out.