One caller last week said his 4WD pickup was making a barking seal noise. First, I must say this was a fun and entertaining caller. He was most proficient and excellent in imitating the sound of a barking seal! Second, Tom and Ray thought it might be the locking hubs making the noise. I agree. That’s a good possibility and probably the first thing to check.
But I think the caller should consider brakes as a possible culprit too, especially if the 4WD truck has any drum brakes. I’ve had this barking seal noise happen after adjusting the brake shoes too tight on a 4WD truck. The noise doesn’t happen right away after the adjustment, it takes a few days of driving before it occurs. And steering quickly right & left can reduce the volume temporarily, even if the barking seal noise is coming from the rear brakes. If the drum brakes have recently been adjusted or replaced, or even if they are old brakes and the shoes are sticking to the backing plate, brakes should be considered. I’ve never had this problem occurring on disc brakes, but if the caliper stuck, I suppose it could happen with discs too.