The parking brake issue has been popular on here recently. From what I gather, the shoes get rusted/corroded and grenade inside the hub, destroying tone rings and making terrible tank track type noises. Might be worth pulling a rotor off to investigate. Axle vent mod is to prevent clogged oem axle vent from not allowing pressure inside the axle to equalize, basically blowing axle seals, which is very costly to repair. The axle vent mod can be purchased from a well known exhaust guru on this site or ou can build your own with toyota barbed union fitting, some old fuel hose and a cheap lawn mower fuel filter. Its a good preventive mod I think. I did it to my most recent titan when it was practically new.