probably the joint you replaced 2 years ago
how true it is, but I've always been told to replace both joints at once. If one is going out, and you put a new one in, any stress is amplified to the older one, because it is more worn, and it kills it that much quicker, so its a vicious circle of swapping them out. If you replace them at the same time, they deteriorate equally, and together last longer.
