If the differential yields a low pitched rumbling sound, then ensure that the proper fluid level, type and quantity is used, then drain the fluid and replace it with the recommended type and quantity of lubricant. Then, check for wear or damage of the differential bearings, have a look at the drive and the driven gears and replace such part of the differential will replace if there is any damage. As with the howling noise from the differential, therefore, first look at the fluid level, type, and quantity, and replace it with the right lubricant. In the same regard, we can look at the differential drive and the driven gears to determine whether the two have worn out or have been damaged in one way or the other and when this is the case, it is only right that we replace them.